How to Keep My Children from Smoking Weed?

Ok for the moment I don't have children. But i do plan on having children someday and well lately we've been studying drugs in school and it got me thinking "I sure as hell do not want me kids smoking weed". So I tried asking about the harmful effects of weed and I just got a bunch of hippies tellin me that alcohol is worse and weed should be legalized. Ok, I don't care, I don't want my children drinking either, and atleast you don't get drunk after 1 beer, with pot your high no matter what. I've looked stuff up and I've seen things like "could cause low sperm count or potential cancer" something something similar to ciggarettes. Look I'm not asking your opinion on weed if you want to smoke pot be my guest, I just don't want my kids to. I'm asking how to keep my kids away from it. And please don't tell me "well if you're learning about it in school ask your teacher" because I know my teachers and they'll think im the one smoking and something about they are forced by law to report it. Whatever I already convinced my girlfriend to stop cause I care about her health and she understood, but hell you know how kids are, I still am one. So how can I convince them weed is bad? Facts would be great thanks

Suggestion:

Well I have a 13 yr old and there are kids smoking weed all around him. I ask myself this question every day. He has all the pertinent facts. He knows if gets caught his life will be miserable. He also knows he can tell me. That sounds contradictory I know. I heard I should ask him if he wants to try pot. Then when he answers ask why or why not without lecturing, just listening. I promised him he could tell me he was smoking or experimented and I would not come unglued but would rather he be honest than find out another way. Hopefully he realizes me finding out another way means losing much much more than admitting it to me himself. I promised no screams or tears but just understanding that there is temptation out there and it is my job as a parent to teach him self discipline and how to make healthy choices. And that there are consequences for making bad ones. Just like the real world.