Did you ask your vet about it? What did he/she say?

I think applesmom had a good idea...calling an animal behavorist. My friend is actually doing that because her Schnoodle pees all over the house. But I'd rather have peeing than fighting.

I wish I had some advice. Good luck.

Oh wait...I just found this site:
http://www.seefido.com/html/rivalry_amongst_dogs.htm