That's fucked up parenting. Nice that you care, but you may want to step back and review this and consider some other approaches. If your son is smoking week, he's at least a teenager. You're preparing him for a police state, not to be self-regulating and responsible. Clearly, zero trust being built in your house.
How long before he figures out the pattern and hides his shit out of the house? Then you have zero potential for oversight and education.
And what kind of example do you set having your own weed, and disposing of his? You think he's not aware of your actions? Please. You're just showing yourself to be a hypocrite.
My folks found a few things here and there. Then it was addressed, not scuttled. Sorry, to lay in on you anon, just don't think you're going to accomplish your goal, and you clearly do love your son to be taking action as you do. Just my opinion, please don't take offense, but there are other ways.