We have a two year old german shepherd/golden retriever/lab mix that has been such a great dog. In the last six months I've noticed that she has gotten aggressive mainly towards men. I took her to the vet and she was very apprehensive being there and wouldn't let the male vet come close to her for ten minutes. The other night I found out she bit the UPS driver. She hasn't been beat and we got her when she was a pup. I want to help her out and figure out what's triggering her before we have to make some big decisions.. has anyone dealt with this or have any pointers? We have four other dogs she does great with but she refuses to let other dogs near.