We don't usually get that kind of question here Mr Nice Guy, since members are supposed to be 18+, according to the rules.
It's hard to know what your parents' attitude is about mj. If they've swallowed the 'party line' about it being a dangerous drug that leads to hard drug use, it may be a waste of time to try and change their mind about it. As for excuses or methods to make them forget about it, I'd suggest not trying anything that involves deceit or attempts at manipulation. Honesty and trust are the foundations of any relationship, and that's your best bet from here on out IMO, even if it means holding off on your mj use until you're on your own.
If you want advice from those closer to your age, I'd suggest joining the marijuana.com forum. The age requirement is lower there, and there are a lot of threads similar to yours.