You've gotten some good suggestions, and I'm sure you've gotten some pm's by now with more. One thing that was mentioned in a post was a suggestion about having someone walk your dog - personally I think this is not a good idea, unless it is the behaviorist who is walking him. If he attacks another dog while on the walk, you would still be liable - and the dog walker may inadvertently take him into a situation that increases the chances of that.
I'm glad that you are seeking the help of a behaviorist. I've seen lots of little dogs who have been allowed to rule the roost - I think that when they are puppies, we think it's funny when the tiny thing acts all gruff and tough, not realizing that we are reinforcing the behavior. My mom had a papillon at one time, and seriously we called him the Anti-Christ because he was such a holy terror. It wasn't the dogs fault, my mom let him get away with far too much as a cute little puppy, not realizing how that would translate into adult behaviors.
Livin in a Newfie Drool Zone