Have you tried a clicker for training? You need to follow the instructions to "load" it first . i.e. some high value (very small pieces of chicken or cheese) scattered on the floor and for everyone they go to eat just "click" and say "good boy/girl" so they associate the treat with the click as a reward.
Then start clicking on the sit command everytime his bum hits the floor and reward with a treat.
When he comes baring teeth, rather than tell him "no" just ask him to sit or leave or something you want him to do rather than just telling him to stop (if you know what I mean) then click and reward.
You might just have one that is trainable!!!
Anyway, we couldnt possible give any more advice until we see a photo of the
demon lovable little one!
