I have a 7yr old male PP who was very much socialized on a daily basis under positive circumstances. When he turned 2, he started to fight with males that would come near. He would not run up and attack them but only fight with males and a very few females. He hates german shepherds, huskies to the one.
The only reason I can see for this is that he was never neutered and thinks he's the alpha dog. Great dog otherwise.
