I've been smoking pot for about 2yrs now (currently 18 ) and i know my mum really suspects it, but for all the wrong reasons! She found a set of kitchen scales in my room (cheapo 1g increments) that a frend bought over as a joke and left behind.
A fuel reciept from a place called Murwullumbah, which she seems to think is weed central..? Funny thing is we refueled there on a trip to Nimbin, which IS weed central.

And the other day i was trying to download the song Addicted To Drugs - The Kaiser Chiefs and she got the idea i was downloading drug movies, which i found rather amusing.
And by far the closest i've ever come, i had my hookah pipe (large free standing water pipe for smoking flavoured tobacco) set up on my deck one nite and they got home early, i panicked and stashed it in the corner, but the coal fell off and started burning thru a plant, which my mum smelt wen she came out. I told her i was having a cigarette, and she didnt notice the giant ornamental pipe in the corner.
Its funny she still wants to believe that i dont do any drugs, a thorough search of my room would reveal baggies of pills, tabs, buds, tobacco, shrooms, speed, and one large hookah pipe. Maybe i'll tell her one day, but her views on drugs are far too irrational at the moment, shes a nurse and still spins the bullshit on any drug as good as a polly.
Think my dad mite have clued onto it tho... He asked me what i was doing in Murwullumbah, i replied water skiing, and he just gave me that nod and left it.