Cindy,

How recently was he declawed?? Unfortunately, cats that are declawed sometimes have behavioral problems such as you described. And since the vet has ruled out any kind of medical problem, you might want to confine him in a small room with his litterbox, food and water. Hopefully, he'll get the idea. If he was declawed recently, the litter might hurt his paws. If that's the case, try either Feline Pine or Yesterday's News until his paws heal.

Declawed cats can sometimes (not always, though) develop arthritis in their paws, litterbox problems, biting (it's their only defense since they have no claws). What I might suggest for the biting is to use a squirt bottle. Everytime he bites, squirt him (not in the face). He should eventually get the hint.

I hope this advice helps. Please let us know how you make out. Good luck.