@nobarkus:
I really suspect there's a physical problem going on with Benny.
I don't. He is resource guarding the chair, and his personal space. He may, or may not be fearful of strangers, but he certainly doesn't want them approaching him for whatever reason. He is completely overwhelmed by recent experiences regarding interactions with people.
I think you (his owner) need to just stop for a moment, and regroup. No one should approach him except for you and whoever lives in your house right now. If someone wants to pet him on a walk say 'no, I am sorry, he is afraid of strangers' whether he is or not. And you need to 're-program' him (for lack of a better word) that it is a great thing to have people approach him, but you have to do that slowly.
Start off dealing with the chair by teach him to be called off of wherever he is sleeping. And no one moves him physically at this point. You call his name and wave a treat around, and until he routinely jumps off the chair as soon as you call his name, then you start to fade out the treat.
There are lots of steps involved in this training, and honestly I don't have the time and energy to write them all out here….a lot of people have mentioned some great books, and there are lots of others. When you call a behaviorist (which you should), interview him or her...make sure what they say makes sense to you. Dominating this dog is NOT going to work...you have to establish trust...if the professional that you are going to be paying doesn't talk about this, look to someone else.