I saw a segment on the dog whisperer of the same thing. He took the attacker by the scruff of the neck and made him lay on his side till he gave in and calmed down. He had the dog that was attacked stand right in front of the attacker. I think what this does is put the attacker in the order of the pack that he's supposed to be in. Anyway, I do agree that a behaviorest needs to be brought in, or maybe look thru these video's and see if you can find one that would help you try to correct this behavior yourself.
http://channel.nationalgeographic.co.../dogwhisperer/