Outtolunch,
The rule he broke was smoking with the kid across the street, and lying about it when I asked him if that's what he was doing.
I let him smoke. I buy them for him as payment for doing his chores and generally following house rules. I am okay with him smoking cigs, but not pot.
When he left the rehab, i asked his counselor if i should continue the no-smoking ban. she said she doesn't condone smoking, but that you have to pick your battles. i tend to agree.