I'm seventeen and my advice would be simply just to confront him about it and say that you know he's been in your stash, and let him know that you're okay with him smoking as long as he keeps his stuff straight, grades and what not, and doesn't pinch your bag. I'd say sometime when the wife is out and maybe when he's 17 or 18 you should smoke with him, a lot of my friends dad's smoke and smoke with them and lets just say kids find nothing cooler than smoking with their dads. Make sure to lay down some guide lines for him, and make sure he's not stupid about it. Think about it this way... If you give him a safe place to smoke at home, he has less of a chance getting in trouble with the law.