i had some friends that were athletes in college,
from what i understand the NCAA tests the entire mens football and basketball teams, and the womens softball and basketball teams. for the rest of the sports 1 mens and 1 womens team is randomly tested in full, and then 1-3 players from all the rest of the teams are selected randomly.
However these tests are not random themselves, they have a set date and athletes and coaches are given notice.
You can pass a urine test for THC (weed) by chugging water all day and night before you go.
Also THC is a lipid soluble drug, so the less fat you have and the more fat you burn the less likely you are for testing positive after recently smoking