Health and safety is a top priority for all businesses. Keeping their workers fit and healthy is in their best interests as well as their employees'. There are many avenues available to employers to guard against this issue of being drug-impaired at work: having a culture of trust and knowing your employees; having good managers or supervisors who can deal with potential issues and report to those who need to know where things can get sorted. It isn't difficult to identify people who both take drugs regularly and are being affected by drug taking. As a secondary school teacher, I could walk into any classroom, or any house, for that matter, and point out very accurately the students who use drugs, mainly marijuana. They think they're fooling you, but they're not. I would suggest that any employee desperate enough to carry around a bottle of synthetic urine just in case they got tested would be easily identified. They obviously have a problem, and should have been identified well before any action was required. 