Most companies now adays, reserve the right to drop a UA, on you if they suspect something's amiss.. It doesn't necessarily mean, they will drop randoms, on a regular basis.. If you are that concerned, lay off what ever it is, your afraid of them finding, and focus on doing your job, and you'll find out, thru coworkers. I have signed them before, and I never had a drop done, it was only that they have the right, and you agree to it.. so keep your nose to the grind stone