Alright I dont know if this has been suggested before but, with the new animal behavior that makes them attack humans if they get too hungry I think that would be something good to have, yes I am aware that you can simply draft them and leave them on that spot although they leave after some time and if you are thinking "But turrets already do that for you" there is a difference between a guard and a turret, a turret is stationary and costs resources while a guard is flexible and can be placed virtually anywhere. Once in a while you get a mercenary which doesnt have many productive skills aside his millitary capabilities, usually I turn them into janitors but I think a guard work would make a better use of them.
Edit: That would also help to handle the new prisoner behavior, I mean what kind of colony leaves the prison unprotected
On a related note, a single turret in a shared prison would solve breakouts. If they were breaking out, they'd likely instantly go and attack the turret before even leaving the room, and it would take a few out itself maybe, but would also explode damaging anyone left. That would probably damage them enough to be easily picked off by your colonists.