Debbie, in my...very novice...opinion. He's having too much control put on him during protection. One of the many things I've learned from starting an adult dog in this sport is, even tho they're adults, they need to be started like they are puppies, and brought along at whatever rate they can handle. I am just now asking Blitz to show any sort of focus/attention during protection, and we've been training for ~18 mos. So no, I don't think the e-collar is the answer. (You all know I've been using one to clean up her obedience...during Obedience. I asked Joel recently about using it for secondary ob. in protection and he said no, not yet.) Personally I think a pinch, to give you control when you need it, and a harness, to actually work him on, is the perfect combination. Just because no one at that club really uses one, doesn't mean YOU can't.
I also think it's high time he stopped working with other dogs. Again my very novice opinion, but with Boris being who he is, watching other dogs bark and slather might very well exacerbate his DA issues. Blitz is brought near the field as the dog before her finishes working. As that dog is being put up and the helper readies himself for her, I whisper "where is he?" She's learned what that phrase means, and now goes up on tippy toe and gets ready to work. If there were another dog out there, I have no idea what she'd do. From day one, Blitz worked alone on the field...treated as an adult that needed it's space, but trained as a baby who knew nothing. And this is with a trainer who very much believes in doing puppy circles. Just my 2 cents worth.