Saw this on the golf channel this evening. Martin Hall had a pretty neat looking tool to keep people from flipping. He took a piece of plywood and cut a 6" square out of one end so it formed kind of a notch. Basically you just set the board on the ground, put a ball in the notch and take a swing, hitting the ball, then the ground while missing the plywood. If you flip, it will be pretty obvious when you smack the plywood behind the ball.