Put up a little doggie gate when you're cooking, that should keep him back.
Is your dragon chewing on someone's car? After all, that's what they are, aren't they? Walk up to your dragon, look him sternly in the eye, and say "Bad dragon, very naughty!" Then, flick him on the nose until he drops the car. It feels important to mention that this costume is not fireproof, so try to steer clear of any fire-breathing! MOST IMPORTANTLY, BE SAFEAt the end of the day, the most important thing is your safety.