I've convinced little kid that if he's ever home alone, monsters will come get him.
Monsters will never bother a child as long as a grown-up is around, but if he were ever home alone, or if he ever left our yard by himself, a monster would probably get him.
This has worked out well because now if he protests when I tell him to get his shoes on, I ask him if he wants me to leave him at home for the monsters and he usually goes and gets his shoes immediately. The few times he's tried to test me by saying he'd stay home, I told him okay and wished him luck with the monsters as I got the keys and walked out the door.
He rushes right out and grabs my hand, perfectly happy to get into the car.
Parenting experts would probably say this is "wrong", but I don't see them lining up to babysit or help out any, so they can stuff it.