This is the problem they are trying to fix at my school (which, their solution, I believe is a problem)
What they did to try to prevent people from smoking in bathrooms is lock most bathrooms, and all others must have the door open. All the time. (Anyone else find this a violation of privacy?) I'd say smoke detectors would work better.
Showing the posters and video of what happens to smokers only works for some people, so that's not a guaranteed solution. We had to watch it in health class, it stopped the smokers in our class from smoking for...a few hours...At least they may consider it in the future though.
There's no smoking zones here, they've made smoking illegal (and subject to fine) within I believe it was 500 feet of schools and some public parks.
Not that any of those things have stopped people completely (sadly) Appearantly some kids sneak out of school and place a coin in the door to keep themselves from getting locked out, go smoke in the woods, then sneak back in.