I think you're the best person to answer that question...
Used to work for a large DoD contractor myself (10000s of employees). We'd have the pre-employment drug test that tested for the usual scheduled substances (cocaine, meth, weed, etc.) and got hired on.
In my instance, there was no fear of being tested again unless we screwed up on the warehouse floor, wherein, we'd have a drug test to see if liability could be shifted.
I think if you've worked for a company long enough, you know when a test is coming... and for what. I highly doubt anyone is getting tested for AAS unless you give them a reason to. It's expensive and not something employers really care about.