As I mentioned in another thread, if it is failing a drug test regarding pot, I think they need to simply sit their arse just like they would regarding academics. Society is sending a clearly different message...including their Toker-in-Chief, Obama...who bragged about having done plenty of that WHILE IN COLLEGE. The media treated it like it made him even cooler. If it had been a Conservative, then it would have been a grave evil.
So, upon a third failed test, then sitting out a mandatory number of games would likely wake some of these Honey Badgers, and Janzen Jacksons up. But I don't think it's right to just kick them off the team.
I'd just get the message across..."You want to be like all the other college kids here...smoking pot on the weekends? Go ahead, but you will indeed be like them in that you won't be playing on this team...until you decide to get your head on straight."