[HisNameIsHarley]

I asked my vet about that because one of my other dogs was doing that months after he was neutered and it drove me nuts. But he said that sometimes it can take several months for all their testosterone to leave their system after their neutered. And also he may simply be doing it to be dominant and if it's simply a behavioral issue just start correcting him when he tries to mount her until he gets the picture that it isn't acceptable.