Welcome to Pet Talk, MarleysMommy! You'll just love it here, and I must say that Marley is a real cutie! I'm so sorry to hear about the troubles you are having with him. It's really hard to pinpoint what causes aggressive behavior sometimes, so don't get discouraged.
My guess, perhaps, would be that if he's been doing this since kittenhood, it could just be a learned play/aggression behavior. It's just more painful now that he's older. Actually, I have read that getting a playmate might help with aggressive behavior in some felines. That may be worth a shot. Bring a kitten into your household and see how Marley reacts.
In the meantime, whenever he does anything aggressive, say "NO!"(or shake a can of pennies, or squirt him with water) and then ignore him for 15 minutes. Praise him and give him treats when he's being nice. You may also want to try some feliway, as it has a calming effect on kitties. Good luck and do let us know how he's progressing!
**hugs**
Karen