This is the reason it is important for the owner to establish himself/herself as the alpha dog among the pack, which is a daunting task when dealing with more than one or two dogs. Without the alpha dog dominance over the situation, and sometimes even with the dominance over the situation the dogs may love you but may not necessarily respect you enough to bow down to the natural instincts of the canine DNA and call of the wild, so to speak. Situations such as bringing a new dog into a home without taking the necessary steps can cause these natural instincts to crop up causing major problems, sometimes even deadly ones.
Each time one adds a new dog to the home, there is a new ranking or re-establishment of the pecking order. The owner's position is equally a challenge in remaining in control as alpha dog. According to veterinarian sources, inter-female dogfights are worse as they can be extremely fierce in protecting their territory. In fact, once a dog experiences the viciousness of an attack, it can take a lifetime to get past the attack if ever. The traumatic experience can cause an otherwise submissive dog to become aggressive and leery around other dogs to the point where the submissive formerly attacked dog will fight instinctively to protect himself/herself from any new dog brought into the animal's space.
Unless the owner provides extensive professional training to help this dog overcome these fears and anxieties, the dog will become a fighter for life thus becoming a danger to other dogs and to people as the dog takes the stance that a good defense in a better offense. The human pack leader must make it clear to the dogs that this type of behavior is neither acceptable nor tolerable. While the alpha human does not realize it most of the time, the weaker dogs look for the alpha human to protect them from the stronger and more aggressive dogs.
Before bringing a new dog into the home, it is important to purchase a crates large enough for the dogs to stay in when the alpha human is not around and to prevent fights. Before bringing the new dog into the home, it helps to introduce the animals in a neutral territory such as a park or friend's backyard a considerable distance from ether dogs' homes. Keep both dogs on leash at all times. Keep them a few feet from each other to prevent either dog from getting close enough to take the initiative to fight. Slowly and with quiet tones, speak to each dog making certain one dog does not receive more attention than the other dog. It may take as many as a few to a few dozen of these meetings before the dogs get to feel some type of comfort zone with the other dog. If it does not appear to be happening, contact a professional trainer for assistance. If it still does not appear as if the dogs will bond as friends then it is time to consider another dog as a canine companion for your dog.
If, on the other hand, the dogs to seem to begin to feel a comfort zone, discuss the issue with a professional trainer before taking the next step which is bringing the new dog home. Just as before, allow the dogs to interact away from the home where both will live and gradually bring the new dog closer to the new house. This may take time but it is worth it in the end.
After making progress to get the dogs close to the house and then indoors, it important to keep both dogs on leashes they can run around with the leashes on their collars. If a quick interference is necessary, it is easier to grab the leash for a firm but understanding correction to allow the dogs to realize you, as alpha dog, will not tolerate this type of behavior.
If unsupervised or at night when sleeping, keep both dogs in a nice comfortable crate with a crate cushion in the bottom and even a blanket with his or her scent so the dogs do not feel as lonely. If the current dog sniffs the crate, this is normal behavior. Allowing him or her to sniff the new dog is one way to acclimate to the new dog's scent in a nonthreatening manner.
During this new adjustment period, never allow both dogs out of their crates together at the same time until it is clear the two will not fight. It does not matter if this adjustment period takes days, weeks, or months. There is no rush on building a trusting friendship between the two dogs. While one dog is out, take time to play with the dog and work on obedience skills such as sit, stay, heel, fetch, retrieve, down, and come along with any other obedience training skills your trainer taught you to use with each dog.
Take time every day to walk each dog and allow him or her time outside in a fenced in area to play with Frisbees or kong chew toys filled with peanut butter or dog biscuits. This will burn off extra energy and allow the dogs to rest comfortable when putting them down for the night.
If possible, have a trainer come out to the house to check on the progress of the friendship between the two dogs. A professional trainer will give you a better idea as to when it will be safe to allow the dogs out together to play without any aggression between them as each vies for your attention. Make certain to equally love and hug both dogs so one does not feel the need for jealousy over the other. In time, both dogs will have the freedom of being great house pals together without fear of fighting amongst themselves.
Remember, there is no set time for this bonding to occur. There is no reason to rush it so take your time introducing the dogs to their new environment as they acclimate to each other.