I've been in the active army for about 2 years and I have never been tested by hair or blood. I've been piss tested 3 times since I've joined, but usually testing goes like this, every month 10% of my unit gets picked at random to piss and every now and then 100% of the unit gets pissed, however even if you get pissed doesn't mean you won't get pissed again the next week. I've seen units piss their whole unit once a week till they felt everyone is clean and their unit is drug free. The problem is you really never know when it's gonna happen.