YES! Ivy does the SAME thing. She never fights when there is no human there. But as soon as a human enters the picture, she snaps and attacks. If you think about it, a human is a very high value resource. We give love, pats, play, walks, and food. We are the beholders of everything good in their lives, so it makes perfect sense that our presence would incite scuffles amongst competing dogs.

Ivy is a number 2 dog. She's very dominant towards Lucky and Gis but extremely submissive towards me. Whenever I see her stalking Lucky (which will lead to an attack if I don't intervene correctly), I recall her and put her into a long Down-Stay. When you see Rusty about to attack, don't reach for him or Blair. If you reach for him, he will most likely attack. Instead, distract and recall him. If his recall isn't reliable enough, keep him on lead. Once you recall him, place him in a Down-Stay. It sounds like Rusty's trying to exert his dominance with unnecessary force. He probably knows you're alpha, but you need to let him know that fighting over humans/resources is not allowed. So anytime you see him getting into that 'mode' (usually head down, hard stare, stalking position), distract, recall, long Down-Stay.

That should do it. Since I figured that out, we've not had an attack between Ivy and Lucky for months now (of course, Ivy and Gis are another story ).