Do the army test hair samples for drugs?
No... I never remember them cutting my hair to tell if I was doing drugs, only the standard urinalysis.
You really can't. Hair tests are over 99% accurate and practically impossible to cheat. If you've used drugs in the last 90 days, they will find out. A standard hair test uses the last 1.5 inches of hair, which goes back about 90 days. Longer hair samples can be taken to go further back in time, but that is atypical.
Certain drugs can be detected in the hair. The best way to pass the test is not to take any drugs. All drugs can be detected in your hair follicles. Drug testing of the hair follicle, is the most effective drug test there is, because everything you ingest, stays in the hair. They can pick up on it even if you are fresh out of the shower.
Of course it will. Most drugs other than alcohol, will remain in hair follicles for the standard 90 day test. And don't be fooled into buying "special shampoos or rinses" A hair follicle test goes into the hair, not on it. They extract the drugs from grinding up the hair and extracting whatever drugs you've used 90 days ago or longer.
Yes. Any drug can be tested using hair samples--using hair from any part of the body. Unlike urine or blood tests which look for metabolites; hair-tests can track use for many months long after the drug and all its metabolites have been eliminated from the body--this is because drugs can be tested by checking protein deposits in hair.