PEM850: I think this might be your fault, but its DEFINATELY not intentional. Before I go on, I have to say my opiniong. NEVER tape your dog's mouth shut. I would highly recommend NOT putting a shock color on. I've heard there are collars that just make a noise and its high pitched and gets louder as the barking goes on. I wouldn't recommend these either. They are more humane, but there is an even more humane way yet.
Your dog most likely thinks it is in charge of your pack, it needs to protect you from the unknown.
You NEED to make sure dog know that YOU are the alpha. I can give you some advice, but I HIGHLY recommend you buy the book: The Dog Listener by Jan Fennell. Once your dog knows that you are the leader, some problems will probably be overcome that you did not even know were problems. (running up to you when you come home etc.)
First you NEED to make sure that you are the leader. There are many ways to do this. I'm not really sure which way would work, as I do not know your whole situation. I have just received The Dog Listener on Thursday and am on page 135 or so. It explains the world from your dogs point of view, and from wolves. Here is a good example. In wolf packs, once they hunt a bear for instance, the Alpha pair will eat first. When and only when they are done to the other wolves get to eat. How you could transform this is putting a cracker near your dogs food while you are preparing it. Make sure it is up higher. Pretend to fish around and then eat your cracker. You are showing that you get first choice from the meal.
Again, I can't say it enough, buy that book or get it from the library, I'm sure it could help you ALOT!