Canine rivalry may occur for one or more of the following reasons:

• A new dog is brought into the home.
• You attempt to be fair and treat both dogs equally instead of supporting the position of the dominant dog and maintaining the hierarachy.
• You give what is viewed as dominance signals to the subordinate dog, such as punishing or removing the dominant dog for threatening the other dog, taking his food, taking his toys, or forcing the dogs to share.
• A dog returns home after being absent for awhile.
• A young dog reaches adulthood (18 months – 2.5 years).
• A younger dog senses that an ederly dog cannot hang onto dominant status.

As human beings, we often want to make things "fair" or "equal", and help out the underdog.  Our natural tendency may be to try to correct problems by making the dogs share toys or do what seems more just to us.  Unfortunately, this increases the problem and confuses the dogs. 

Typically, age will command respect among dogs before size.  Just as adults run the home and make the rules, so might the older dog.   A dog that is in tact will usually expect a higher status than a dog that is spayed or neutered.  If you are introducing a new dog to your home, you should assume that the resident dog will be dominant, unless you observe otherwise later.

To determine which dog is dominant, watch which dog goes through the door first, or gets closest to you. Which dog can take food or toys from the other dog? Which dog walks ahead of the other dog(s) when out walking? Which dog gets the best sleeping spot? That is most likely the dominant dog.

Dominance may switch in different situations or environments. One dog may be dominant in the yard, but not in the house. Positions may also change over time as dogs come into adulthood, or become aged.

 
What to Do About Canine Rivalry Problems

 

You should not try to interfere with or choose which dog is dominant. The dogs establish the order among themselves. If you try to change that, you will inadvertently increase the problems and fighting.

Dominance is most often established with body language and verbal communications that do not result in any actual injury. You will often see these 'practiced' in play wrestling. Behaviors such as staring, growling, lip curling, leaning over, and the position of the tail and ears (up is usually a dominance signal, down is the opposite) are all communications about who is in charge.  Other displays of dominance include: rush and take-down, rolling the other dog over, or resting the head over the other dog's body.

Cowering posture, head turning, rolling over, exposing the belly, and looking away/breaking the eye contact are physical ways of communicating submissiveness.  (Interesting note:  When your dog looks 'guilty' by crouching and slinking away, your dog is really saying, "You're the boss." and communicating submission.)  Some submissive dogs may  even urinate to display submission. 

When a new dog enters the home, or when mixed signals are sent (for example, if you repeatedly take the dominant dog’s bone away and give it to the other dog), conflict can arise. One dog may snarl, growl or snap at the other. This can escalate into fighting which may result in injury.

 

Here are some do’s and don’ts for canine rivalry issues:

• Do not expect new dogs to get along quickly. There is an adjustment time needed and sometimes the first day or week can be the worst. 
• Respect your dog’s breed and innate disposition.  Some breeds of dogs have been bred specifically to be guard dogs or fighting dogs and thus may be more prone to seek dominance or exhibit dog aggression.  If your dog has had dog aggression issues in the past and you wish to adopt another, seek professional help.  
• Be sure to introduce new dogs properly, beginning with a meet on leash in a neutral location, lavishing praise for non-aggressive behavior.
• Do not treat the dogs equally or punish the dominant dog (i.e. save the underdog).
• Do not get in between fighting dogs, or you may get bitten. (This is known as redirected aggression. Your dog isn't intentionally biting you; you are just in the way.). Throw a blanket over fighting dogs, bang pots and pans, whistle, clap, spray them with water, go out and ring the doorbell, but do not get in between.
• Realize that a dog staring at another dog after a squabble is still challenging that dog. Remove the dog that is not dominant to another room for a brief time out until things cool off.
• Do not remove or punish the dominant dog. This communicates the wrong hierarchy message and confuses the dogs about who your view as dominant. 
• Never yell or scream or hit dogs for fighting. This will do nothing to resolve the issue between the dogs and can increase aggression. Dogs may fear an emotionally charged person, but they respect calm leadership.
• Reward friendly and peaceful behavior whenever you see it.  
• Reward your resident dog when a new dog is around, with the goal of conditioning your dog to associate positives with the new dog.
• Always respect the hierarchy: the dominant dog eats first, leashes first (gets the longer leash), goes out the door first, gets petted first, gets the ball first, etc.  When you back up the pack order, it helps keep the structure and peace.
• Spay or neuter all dogs as soon as it is appropriate. 
• Do not interfere with small squabbles or dominance issues (for example when a dog takes a toy from another dog).  Usually, these resolve on their own. If a spat begins to escalate, try distraction techniques like immediately taking all dogs outside.

Please remember that you and your family should be viewed by the dogs as dominant over all canines in your household. This is not done with force, it is communicated by body language and leadership.  Pack leadership can be clearly communicated to your canines by hierarchy signals: you and your children always going through doorways first, eating first, getting the comfiest spot, etc.  If your dog is threatening anyone in your family or over-guarding people or items, there are things you can do to correct that.  For best results, consult professional help from a dog trainer or an animal behaviorist.  

Don’t forget to enroll your dogs in obedience classes also.  Not only will you bond better with your dog, but you will reinforce your natural leadership and authority.