Dogs, like wolves, are territorial by nature. They have a pack or rank order which include a pack leader. Every dog in the pack knows its rank. When fights begin, dogs will gang up on the weaker or newer dog. Some lower rank dogs will turn and run at the mere sound of a fight.
Dogs can sometimes be aggressive. Once attacked, a dog will always be leery of meeting new dogs. Many will automatically become fighters the rest of their lives.
When it comes to sexes, there is some evidence to suggest that having a neutered male and spayed female is best combination. The next best mix is probably two neutered males. The least desirable combination is two females, and it doesn't matter if they're spayed or not.
The biggest mistake a dog owner can make is not really getting to know the new dog and relying on the resident dog to break him into his new surroundings. Sometimes the purpose of getting a second dog is to keep your resident dog company. And it's easy to let the dogs hang out with each other and become friendly. But what's more important is making sure you're spending enough alone time with your new dog. If you don't bond with the new dog by itself, then the new dog bonds with resident dog and the owner doesn't really get to know the new dog.
WAYS TO INTRODUCE THE NEW DOG TO THE RESIDENT DOG
- CHOOSE A NEUTRAL LOCATION
Once you've made the decision to get another dog for your household, you should choose a neutral location to introduce to resident dog to the new dog. Introduce the dogs in a neutral location so that your resident dog is less likely to view the newcomer as a territorial intruder. Each dog should be handled by a separate person. With both dogs on a leash, take them to an area with which neither is familiar, such as a park or a neighbor's yard. If you frequently walk your resident dog in a park near your house, she may view that park as her territory, so choose another site that's unfamiliar to her. We recommend bringing your resident dog with you to the shelter and introducing the dogs before adopting the new dog.
- USE POSITIVE REINFORCEMENT
From the first meeting, you want both dogs to expect "good things" to happen when they're in each other's presence. Let them sniff each other, which is normal canine greeting behavior. As they do, talk to them in a happy, friendly tone of voice - never use a threatening tone of voice. Don't allow them to investigate and sniff each other for a prolonged time, as this may escalate to an aggressive response. After a short time, get both dogs' attention, and give each a treat in return for obeying a simple command, such as "sit" or "stay." Take the dogs for a walk and let them sniff and investigate each other at intervals. Continue with the "happy talk," food rewards and simple commands.
- BE AWARE OF BODY POSTURES
One body posture that indicates things are going well is a "play-bow." One dog will crouch with her front legs on the ground and her hind end in the air. This is an invitation to play that usually elicits friendly behavior from the other dog. Watch carefully for body postures that indicate an aggressive response, including hair standing up on the other dog's back, teeth-baring, deep growls, a stiff legged gait or a prolonged stare. If you see such postures, interrupt the interaction immediately by calmly and positively getting each dog interested in something else. For example, both handlers can call their dogs to them, have them sit or lie down and reward each with a treat. The dogs will become interested in the treats, which will prevent the situation from escalating into aggression. Try letting the dogs interact again, but this time for a shorter time period and/or at a greater distance from each other.
- TAKING THE DOGS HOME
When the dogs seem to be tolerating each other's presence without fearful or aggressive responses, and the investigative greeting behaviors have tapered off, you can take them home. Whether you choose to take them in the same, or different vehicles, will depend on their size, how well they ride in the car, how trouble-free the initial introduction has been and how many dogs are involved.
If you have more than one resident dog in your household, it may be best to introduce the resident dogs to the new dog one at a time. Two or more resident dogs may have a tendency to "gang up" on the newcomer.
- USE CRATES
Put the new dog in a dog crate in the house where the other dogs can go up and look at and smell it. If there is growling, correct the older house dogs for showing any sign of aggression. If need be, put prong collars on the house dogs and let them drag a leash. If they growl, give a hard correction. There is no reason to rush the introduction of a new dog into your home. Let the dogs' only contact be after several weeks. During the first weeks the only time they are around one another is when they are in dog crates. After enough time passes they will begin to learn that this is not really a stranger, but a new member of the family pack. So for the first three weeks (or as long as it takes) when you want the new dog to be loose in the house, the old dogs are either in a different room or in their dog crate. Over time it will become obvious that the new dog is now a pack member. But remember not to rush the process.
- WHEN TO GET HELP
If the introduction of a new dog to a household doesn't go smoothly, contact a professional animal behaviorist immediately. Dogs can be severely injured in fights, and the longer the problem continues, the harder it can be to resolve. Conflicts between dogs in the same family can often be resolved with professional help. Punishment won't work and could make things worse.