Over the last few weeks Ive gotten three separate calls about dogs that hate each other and cannot be in each others presence without a fight breaking out. In every one of these cases it was not aggression which was the issue - in fact all dogs were far from aggressive. They just hadnt established a working relationship yet.
Dogs that have never met each other need to learn about each other and figure out their relationship before they can become happy pack-mates. In two of the cases I just worked on, it was a younger dog meeting an older dog. The young pups just wanted to play, play, play, while the older dogs just wanted their space respected. These dogs can absolutely peacefully coexist but we need to control the situation while they learn how to relate to one another.
I used leashes to stop the puppies from jumping into the older dogs space and gave them time to adjust to each others energy. The pups learn that not every dog wants to play and that they can have relationships with dogs that dont include tackling and chasing, while the older dogs learn to put up with this high energy puppy and that the humans in the pack will make sure that their personal space is respected.
It can take some time, especially if the dogs have not been well socialized. One thing that always helps is walking the dogs together. Nothing unifies dogs then bringing them together as a pack on a nice long walk. This give them a positive association to each other doing something they both love. The walk should be structured with all eyes forward. I find if we get their bodies moving forward, their minds soon follow. The walks give them a positive association with one another and are a great stepping stone to building a non-confrontational relationship.
If we separate the dogs, and dont help them get to know one another in a positive light, they will never get past their initial state of mind. Yes, there are some dogs that just will never get along but if we take the time to help them move past their high-energy first impressions, we may watch them become friends - or at least learn to coexist comfortably.