Almost every college in America drinks alcohol and smokes pot. I completely understand your concern, but there are some things that you can do that may help your son avoid smoking pot.
- Commuting: This may help him avoid smoking, but it all depends on how far the drive is. If it's a reasonable drive, then this would help him in the long run.
- Be more strict with him: Now, if you really want him to avoid smoking, then you can give him a call every night via face to face chat to see if he's smoking or not. He may not like it, but I'm unsure of how trustworthy he is. He can just say that he's not smoking thru a text message, when he's really doing it.
- Understand that it's on him if he makes a bad decision: This is the harsh truth to reality, but you could possibly give him a mind changing talk that may get him thinking that this wouldn't be good for him in the long run. But, every time he smokes, he's always going to regret doing it later on in life if a video gets posted online of him doing that.