Our friend's dog Ruger and my Willy do that sometimes, but I dogsit him and he is at our house alot, so they just have to get over it. I think it's pecking order and we pretty much ignore it. If it gets out of hand we yell at them to just stop it and they go their own way. What's funny is, if Libby is not involved in the mix, Willy will just follow Ruger around like his big brother, no problem. But if Libby is there Willy thinks he needs to protect her. I'd say chill for now.