you need to watch the dog whisperer. you tube has vids if you never heard of or saw the show, frigging guy is amazing with aggressive dogs, most of the time its fear, not that they are viscous, they seem to think you are weak, and need them to protect you, (you need make it clear to the dog, with out words mind you) who the pack leader is.
the younger they are when you nip this in the bud the better, you seem to know that already tho. good luck, still a cute pup.