I think it really depends on the dogs. Take Leather for example. She is very very aggressive and will not tolerate other dogs. Yet, once she gets used to the dog, she becomes very attached to it, and she will be a good friend to the dog if it does not bother her. She grew up with my old female dog, Stitch, and they formed such a great friendship. When we moved, she formed a wonderful friendship with the neighbor's female dog Koda. She also had a nice female elkhound friend. I've only ever seen her get along with one male. She doesn't like males because they are too "sniffy" or they try to mount her. Years ago, when my dad was going to breed her, he had a Hell of a time with it. He couldn't find ONE signle male dog that could mount her wihtout getting attacked. I'm glad for that.

I plan on having a catahoula leopard dog in a few years, and maybe a year or two after that I plan on getting another GSD. As much as I would LOVE two males, it's doubtful that it would work. Both are aggressive breeds and most of their breed don't tolerate members of the same sex.