If you want him to be in on your hobby, maybe you should have your wife present it to him as something that she also gets a lot of satisfaction from. I told my dad, and he is very supportive of MMJ activism, even though he does not smoke himself. He's just happy I've found something that makes me happy, and isn't that what any dad would want? Who the heck would turn in his own daughter? Just make it very clear that he is not to continue on the gossip chain!
Involve as few people as possible, but I understand that sometimes you have a close family member or lifelong friend who you are willing to take that risk for.