They do have a zero stop so you can return to your zero setting. Can they be accidently turned? You better believe it, they turn easily. You have make it part of your routine, just like not getting caught on top magnification in close cover or at something hopeless on an adjustable objective, or an empty chamber when you thought you were live, or a safety on when you thought it was off. There is no doubt that some people are better off with a straight Duplex, fixed power scope without AO though.
My CDSs came with a straight MOA dial without yardage marking and no cap for the elevation because it doesn't fit with either dial installed. If you took the dial off you can see that the threads and rubber seal are still there, so I suppose that a taller cover would thread on if you wanted to disable the CDS function. Actually, that would even make sense if you flat out know that you won't use it. I wish the elevation dial had a lock.