After the first bite, you should have found a trainer and not let him unsupervised.
Can you find a positive reinforcement trainer to work with you on this? It sounds like your dog does not have the proper socialization and training to know when a real threat is present.
Danielle, owner of...
Fraggle Rock Collars
Fraggle Vom Richcreek CGC CA
Sir; Rescued APBT
Red Dog's Reconnaissance Man CGC
General Patton Vom Winter Storm