I took a class in college called "drugs and society" taught by a psycologist, and one class all about marijuana. It's stored in fat cells for a period of 30-90 days. The biggest area for fat is in your brain. Therefore excersizing(?) will not help much. I've passed probation tests, job tests, and airmen certification tests. All use piss tests, but the biggest key was drinking lots of water for at least 7 days, preferebly 14 days, and taking one of those over the counter drinks at head shops that only mask the THC. I've heard Niacin helps but leaves your skin red-flushed and hot waves, but haven't tried it.
Hair tests, I've learned from that class, can tell what drugs you've used to the day. So if you have long hair that would take 3 yrs to grow, then they can tell what drugs you've used for 3 yrs to the day. Shampoos have no affect. If you shave your head, then they take an ear hair, nose hair, chest hair, pubic hair, arm pit hair; anything they can get. If they can't find one hair, they will reschedule for few days later and they will find out. If you show up still no hair, then auto fail.
Just some things I've learned from Wastern...I mean Western Mich University.
I may be wrong, misinformed, or taught with bad info, but it works and sounds reasonable...aka: common sense