High Tech Safety.

This wee ball is supposed to keep me from driving through the back of the garage. I haven't actually driven through the garage yet, but that's no thanks to the ball, which is not properly adjusted.

The idea is to stop when it touches the windscreen but, since the string is too long, that doesn't quite work. I could get up on the ladder to shorten the string, or I can keep running the front bumper into the bag of fine sand that's sitting on the floor.

Any guesses on the likely short-term solution?