It seems to me that he gets quite a bit of satisfaction from not being caught (or being naughty and not being caught), and you get some sort of satisfaction from outsmarting him. If this cat and mouse game is the underlying dynamics of your relationship, then you first need to change that. Be equal partners, don't be his boss or persecutor (as evidenced by the request that he fess up with his parents), and he needs to learn to be responsible and mature.