My two GSDs play rough it looks like they are fighting but they are just playing when one plays to hard the other will walk away, the only time they get nasty with each other is if we have visitors come and we shut them in the garden together for a few mins till they cool down then they fight to get to the doors to get in but never bite each other they do the same when we go out and get them out of back of the van i think thats a little jealousy as both want to get out same time and we need to put leads on them, so one comes out before the other, sorry cant be more help.