Technically, a urine test could be said to look back a couple of months.

Hair tests aren't that much more than urine testing. I think its about $50 on average for a basic urine test (price goes up as panels are added) and $75-90 for hair.

The fingernail test is a last resort that I've only seen once and the person had no hair from chemo. Most of the time if you shave all your hair, you will get a refusal to test. That's not how to beat a hair test, you can try to clean it using several methods listed in this forum.

The threshold for a hair test for THC is 3 sessions in 90 days with 1 & 1/2 inches of hair.