I have two males together (yep, both unaltered!), a flat coated retriever and a basenji. I was going back and forth with the same things, but I'm a male person. My flat is the oldest, but he is a very soft boy to work around. He has never gone into a fight, because when another dog is growling/getting into it, he backs off immediatly. So I hardly think it's going to be any problems with male/male here. Others might, every dog is different.
