Occured to me that forcing lock on holster via policy may be a security contradiction akin to the old writing down a forced too complex password on sticky notes, i.e., that user, tired of the unit constantly locking after placing in holster, rather places on desk/table and is more likely to forget it. Any comments?

Force a lock after a timeout if you want it locked. Then they have to hit a key every 1/2/5/10 mins to keep it unlocked.

Sorry - should have mentioned that it already has forced timeout for no more than 5 minutes