The business I work for is having an issue with one of our employees and marijuana use. We conduct regular/random 5-panel drug tests and normally, we don't mind our employees testing positive for marijuana, as long as they're not under the influence when they come to work. However, lately we've been suspecting that one of our employees has been smoking on his lunch breaks. This particular employee has been with our business for quite a while, and we would prefer not to fire him without proof of his behavior. Is there any way to drug test for marijuana and know if the employee has used within a few hours? Or do we have to rely solely on his smell and behavior?