I have a 3 month old pitt myself who does the same thing, you need to tell him no in an assertive voice than hand him something acceptable to chew that is his, like i use a nyla bone...it works pretty good. another thing is if that doesnt work submit him/her, what i mean is you turn the pup onto its back or side not rough just assertive, then you place your hand on its chest holding it down while your above him. wait til the puppy submits by no longer squirming. what this does is asserts you as the dominant leader in the pack(family) and lets him no that you are the pack leader and dont approve of his/her current action. hope it helps