I think it would help you if you made yourself a bit more familiar with 'weed'.
You see, unlike dope, weed is not a physically addictive substance. What that basically means is that there is no such thing a weed 'junky'. If one becomes 'addicted' to weed it's purely a mental addiction. Or an attachment if you will.
It's like when you just can't stop eating cookies cause they taste so good. But every time you hit the scale you gained 5 pounds...
To be perfectly honest, i think your husband doesn't think anything of smoking weed and feels it's about on the same level as smoking cigarettes... not 'harmless', but not exactly something to be ashamed of either.
You say that you are convinced that he can accomplish anything he wants if only he stopped smoking weed.
I hope you realize this is a paradox all by itself. To be perfectly frank i think you are just dreaming out loud and telling us about the guy you 'wish' your husband was. No offence, but if you can't just quit smoking pot i doubt you can accomplish all that much. Furthermore, weed puts you in an emotionally comfortable state of mind (cool, relaxed), but it doesn't make you excessively lazy unless you are prone to laziness.
Why exactly do you hate it when he smokes pot?
Why is it necessary to 'teach' teenagers not to smoke weed? Shouldn't they find this out all by themselves? You can instruct someone on the downsides of smoking pot, but that's about it. Prohibition just makes the goods more valuable as society as a whole has shown countless times in the past. If your kids WANT to try pot they will and there is frankly not a damn thing you can do about it short of locking them up in the attic. Which would imho be a LOT more damaging to their psychological health than a joint.
If i catch my kid smoking pot i'll tell him about the bad stuff, ask him not to do it in the house and make it clear that his 'habit' isn't going to be any kind of excuse for slacking off on his grades and schoolwork.
My point of view on this is that putting kids into a protective box is just making them weak mentally. If you just allow them to experience certain things and experiment on their own without the fear of being "busted" and punished BUT always make them live up to their responsibilities then they will grow up with self discipline. They will know they are allowed to party all night long, but also must show up bright and early for work the next day.
That's SELF discipline, and you can't teach a kid that by saying "no this is bad".
Back to the OP. Your husband is an ADULT, if he lacks the self discipline to disallow a very mild drug like 'pot' to take control of his life then i fear he is going to run into a lot more trouble than just pot.
I have a suggestion which you can try.
Make a list of all the things that bother you about your husband. The things you believe are directly related to him smoking pot. BUT exclude the fact that he smokes pot. For example... he might get lazy when he's high. Or he might become unaffectionate... perhaps you feel his career is suffering because of it. Whatever you can think of, make the list.
Now next you need to have a talk with your husband. Tell him that you are no longer going to nag about him smoking pot, you are no longer going to 'punish' him in any way for it.
BUT! And it's a big but. In return, he has to make amends on the things on your list. If he's lazy, he needs to stop being lazy. If his career is suffering he needs to make more of an effort, etc.
"Ok honey, i don't mind if you light one up... but i still want you to help me with the dishes afterwards ok?"
Something like that!
Now if he agrees and makes a positive effort. The result should be that ALL the negative affects that you believe are attributed to his pot addiction will be negated... but he will still smoke pot.
If you find that that fact still bothers you even after he makes amends and improves his life, than you have an irrational aversion to pot, which is i guess not a real problem, but it isn't exactly rational and being irrational is never a good thing.
But if this works out for the best, he may actually quit smoking pot all together OR drastically reduce to a casual smoker.
You see, i don't believe that smoking pot is his 'real' problem. I believe that him smoking pot is your problem. His real problems are most likely a dissatisfaction with something in his life. Perhaps he feels bad about being lazy, he feels bad about hiding it from you, lying to you, he feels bad about being an underachiever, etc. Whatever the cause, if you help him improve these things (by using his attachment to pot as a motivation) he might simply stop feeling the need to use pot to escape from reality and either reduce to doing it just for fun every once in a while or just getting bored with it and stopping all together.
The reason why i say this, is because when i was about 18-19 i was smoking CRAPLOADS of pot. Why? Well to be honest i had little or no life. My dreams were unanswered. I didn't have a good job, i didn't have the self esteem i wanted etc. But then i changed all that, started making more of an effort... and completely unaware of it myself, i started to smoke less and less and one day... i just got bored of it!
Now it's not like i never smoke anymore. I do, this weekend i was at a festival and i had a smoke, but before that it had been two years and it never even bothered me one bit. Days, months, years passed and it never even entered my mind!
If your husbands pot habits were something similar. Would it still bother you?