I don't know when you joined, but since the late 80's, everyone gets tested the morning after they arrive at bootcamp. After that, it's supposed to be a certain percentage of the personnel over a years time, randomly.
By the way, marijuana is illegal, whether you like it or not. Alcohol is not illegal. I'm not saying it's right or wrong but I will say this, the stuff (marijuana) makes people flat out lazy. Our society is ate up with laziness as it is, people sitting around all day, collecting wellfare and food stamps, in government housing with no desire whatsoever to get a job. The last thing we need is to condone them smoking a substance that will only make them even lazier, and eventually lead to medical problems that myself and the rest of the working population get to pay for, on top of every thing else we support them on already.