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How To Handle Interdog Aggression

by Dr. Mark J. Nunez

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Interdog AggressionInterdog aggression is a very common problem that I am asked to help with. I am speaking specifically about dogs that live in the same home, not the dog aggressive dog that wants to go after every other dog he sees who does not share the same address. I have known people with multiple dogs that are never allowed to be around each. This one’s in the garage, that one’s in the bedroom, and the other one is outside. They all rotate places/positions through out the day, but they are never in the same place at the same time. What a miserable way to live!

The most common time/age of onset for this issue is when a dog reaches 2 yrs of age (give or take 6 months). A 2 year old dog is the equivalent to an 18 year old human. This is when they, and we, reach social maturity. Many people get lulled into a false sense of security with rambunctious young dog by thinking, “he’s just a puppy, he’ll grow out of it.”

Unfortunately, this is not the case. Little problems end up becoming big problems when dogs reach social maturity. The reason being is that these dogs are in a struggle for status and control within the group in which they are living. Notice I said THESE dogs and not ALL dogs. Not all dogs are struggling for status, I am speaking only of those that are. The issue can be initiated by a younger dog that is reaching social maturity and who wants to move up on the “chain of command,” or by an older dog in the household that sees a younger, maturing dog as somewhat of a threat.

Context is everything when interpreting canine behavior. For example, if dog A reacts to dog B as if there is a challenge being presented, but dog B is simply approaching to greet dog A, dog A is acting inappropriate and out of context. If dog B, however, is staring, has his hackles up, is putting a paw on the shoulder of dog A, is growling, snapping, and snarling, then dog A’s reaction would be considered appropriate for that given context. Make sense?

Now, the degree of dog A’s reaction must be taken into account. If dog B simply stares at dog A, and dog A goes into attack mode and wants to rip dog B’s head off, this is inappropriate and out of context. A stare should only evoke another stare, or maybe a slightly more intense response like lifting of the head and a stiffened body posture, raise hackles, growl, scratching on the ground, etc… not an attack. Dog have social rules just like we do. This would be analogous to walking over and punching someone in the face because they looked at us. Huh, come to think of it, that does happen in humans, and it is certainly considered inappropriate by most.

The most common scenario that leads to interdog aggression involves a younger dog that had no obvious problems as a puppy, but is now reaching social maturity and begins to challenge an older dog in the household. There is almost always no history of abuse or neglect involved what-so-ever. Many of these challenges are subtle and may go overlooked by owners. They include, but are not limited to, lying on the other dogs bed or “space” or blocking access to these areas; stealing food, treats, bones, or toys; pushing past the other dog to get in or out of a desired space (house, car, etc…), or standing perpendicular to the other dog (the 2 dogs make the shape of a T) with a stiff posture and resting the chin or paw on the shoulder area of the other dog.

Alternatively, the younger dog may not do anything at all. The older dog in the household may sense the changes that the younger dog is going through and preemptively begin to react and assert status and/or become aggressive.

In general, a dog that is challenged can react in 3 different ways:

1. He can defer/submit to the dog issuing the challenge by rolling on his back, urinating, avoiding eye contact, licking his lips while holding his head low, and allowing the other dog to do things first and have the best resources. I want to stress that this dog is happy and content with the arrangement. It’s the humans that have issue with it.
2. He can fight back and one of the 2 dogs submits and the end result is accepted by both dogs. There may be a “changing of the guard,” or there may not be. Either way, the boundaries are tested and both dogs are fine with the out come.
3. Both dogs can continue an ongoing struggle for status and neither one are willing to “give up.”

I would like to take a moment now to discuss the popular view point of “dominance” or “alpha dogs.” While there is some validity to this mind set, it is not absolute and there are MANY variables involved in canine relationships. Remember when I said canine behavior needs to be interpreted IN CONTEXT? Well, context is constantly changing. One dog may be “in charge” while the dogs are indoors, but another dog takes over when they are outdoors. One dog may assert himself more when people are around, and be more submissive when there are no people around. There is even variability concerning which people are present. Dogs can react one way when “mom” is present verses when “dad” is present. Also, as the dogs ages and health status’ change over time there can be changes in who is the top dog.

One special note about people. Many times we cause problems by meddling in our dogs’ affairs. For example, we have a dog and decide that he needs a companion. So, we go out and get another dog. We want the new dog to “feel at home” and to feel loved, so we shower him with attention and give him free roam of the house right away. If our older dog takes a toy away from the younger one, we take it from him and give it back because “that’s rude.”

This can be the other way around as well. The younger dog may take a toy away from the older dog and we intervene because of the social rules that we HUMANS follow. Both dogs are more than likely okay with whatever was taken from him, but we start to impose out social norms on the situation and cause confusion. The bottom line is, in the beginning, stay out of it! Let the dogs work it out on their own. Resist the urge to play referee by enforcing the rules of fairness.

So, what do we do when we have dogs that live together, yet want to fight all the time? The first thing is to start to reinforce the position of the dog that is best able to hold his social status in the event of a fight. In other words, reinforce the biggest and baddest. Well, not always the biggest either, intensity and confidence also play big roles. This may not be the dog that YOU think should be on top. Leave your personal feeling out of it because that will only lead to a serious fight, potentially to the death. Give this dog attention first, affection first, feed him first, etc…

SOla Nigel Play


Two cautions need to be issued here. First, never, under any circumstances, should you physically punish these dogs. This will only serve to increase their levels of stress and they could come back at you. Once a dog figures out that teeth are pretty motivating when they touch human skin it can be difficult to get them to not use this against us. Second, never reach between 2 dogs that are fighting. You will get bit, you will get hurt, period. If you have dogs that you know could end up fighting, always have them on leash when they are interacting, preferably muzzled or at the very least a Gentle Leader. Have a broom, tennis racket, or some other such object to place between them. A bucket of water or a hose also helps. Also, throwing a blanket over them helps to separate them.

General Rules to Follow:

1. All dogs involved should be separated and confined separately when not directly supervised. The aggressive dog should be confined to the less desirable space (i.e. a spare bedroom vs. your bedroom or the basement vs. the kitchen). All other dogs should have free reign of the house. If there is more than one aggressive dog, they should be kept separate and the non-aggressive dog/dogs are given free reign of the house. If they are all aggressive, they should be crated in different rooms or confined in different rooms. Do not crate dogs that are aggressive towards each other in the same room.
2. Put bells that sound different on each dog’s collar. This is a great way of keeping track of who’s where without having to actually have your eyeballs on them constantly. This doesn’t mean relax your supervision. It just means that you can now employ your ears to help supervise.
3. Choose the order in which you are going to reinforce. You may need the help of a behaviorist to assist in making this decision because it is a critical one. Remember, what you think is fair is irrelevant. Here are some hints to help you with this decision:

  • If you have a young dog that starts to slightly challenge a slightly older dog, the older dog snarls and does not back down, AND most of the time the younger dog withdraws the challenge and backs off. The older dog is larger, stronger, and of equal health. Reinforce the older dog over the younger.
  • The older dog thinks the younger dog is challenging him, but the younger dogs is not. The older dog is much older, weaker, and smaller than the younger dog. Reinforce the younger dog.
  • The younger dog IS actually challenging the older dog and is becoming aggressive about it. The older dog fights back and does not want to defer, yet the younger dog still does not back down. The older dog is arthritic and a bit weaker, but they are pretty even in size. Reinforce the younger dog.
  • One of the dogs is actively challenging the other, but the receiver of the challenge does not go back at the challenger. In fact, the dog that’s being challenged defers by rolling on his back.

The challenger then proceeds to go in to the kill even though the other dog is obviously submitting. This is a dangerous situation. The dog that submitted needs to be reinforced (feed this dog first, let him outside before the other dog, giving him a treat or toy first, walking him first, playing with him first, grooming him first, and so on. You can also have the dog sleep in a crate or on a bed in your room or on your bed, whereas the other dog is banished to a room or crate outside your room) in this situation. This will not be easy to do, but if you cannot give this dog some status he will eventually get, at the very least, severely injured. This type of aggression is abnormal. It is inappropriate and out of context. Do not take this lightly! I have seen dogs kill each other in this situation. If you cannot give the submissive dog some status you have 2 choices: #1 these dogs are to be kept separated at all time or #2 you need to find a home for one of them. If the challenger is placed in another home he is to be the only dog in that house.

4. All dogs should be fitting and desensitized to a Gentle Leader face harness. The Gentle Leader is a great training tool that will give you great control over the muzzle of all dogs involved. The dogs should be gradually reintroduced to each other while no special attention is being given to any of them. Having them sit together (but far enough apart that they cannot connect if one decides to try) in the same room is a great exercise. Be sure to reward the dog that is relaxed and non confrontational. If the aggressive dog stares at the submissive one, mild aversive therapy like a water gun or foghorn can be used to discourage that behavior. If the submissive dog stares at the aggressive dog, ignore it and allow it to happen as long as the aggressive dog does not growl. If the aggressive dog growls, use the water gun or foghorn. If the aggression gets worse, remove the aggressor and and put him in a “time-out”. If the submissive dog stares at the aggressive dog and the aggressive dog looks away, reward (with a food treat and praise) the aggressive dog for deferring AND reward the submissive dog as well. This is the behavior that you want from both of them.

One final note. There are many people out there that are not all that familiar with dogs and have never really seen 2 dogs REALLY playing. Dogs can spar and wrestle with one another, with growling, and teeth baring. This is normal. A lot of people misinterpret this rough play as aggression. This is a video of my guys, Gus and Roxy playing. This is a very tame play session. The dogs in the title picture of this post are just playing. It is important to not over react to these situations. Your stress/tension can be misinterpreted by one or both/all dogs involved.

These are the general rules to follow when dealing with interdog aggression. In order for true progress to be attained, you must also have all dogs consistently deferring to you. Sign up for my tips at the top right hand corner of my home page and I will send you a copy of my book How Dogs Learn and How to Actually Get Your Dog to Listen to You. This will cover deference and how to achieve it. All dogs should also be examined by a veterinarian to insure there is not underlying medical cause that could be responsible for seemingly sudden behavior changes, properly exercised and have undergone obedience training.

Thanks for reading, and please do not hesitate to ask questions 🙂 .