I don't understand the need to test randomly. An employer should just send someone when they have suspicions of drug use. Don't tell me that you wouldn't notice a meth tweaker in your work group. A stoner with red Chinese eyes? A lethargic downer pill popper? A fat radio show host? Well, it's hard to tell over the radio.
All these tests are really quite expensive when added up. I suspect that the costs are not derived from corporate profits. Not to mention the people I know who can pass these tests everytime even though they use drugs. That just makes the whole thing laughable.