Hiding in the closet.
I know of one teacher who got wind that the class were planning on hiding in the closet, so as he walked into class, he casualy walked over to the closet, locked it, sat down and had a peaceful session with the few that couldnt fit into the closet!
Daring, but cool!
I know of another, where the class were plotting something, so the teacher asked a substitute to walk in as if the sub was taking the session – giving the kids a feeling of “what a waste”. After a couple of minutes the real teacher walked in!