PROPS DON"T FALL OFF. They will spin off if the engine suddenly stops. This is due to a lean condition that causes a back fire. If the prop is on tight enough to stand up to the torque of the starter, then it will stay on the engine until the engine suddenly stops. If you properly tighten the prop, it will stand up to a lot more strain of a sudden engine stop, but a back fire will almost always spin the prob loose.

This is kind of like running your car off the road and hitting a tree. It will dent in the bumper. The fix isn't to make the bumper stronger, but quit running off the road and hitting the tree. Fix the problem, not the result.

Don