They don't, really; and they fall off pretty easily.

I used to work with a friend who asked me to let him know if I ever killed a deer with my vehicle. The only time I ever hit one, I wounded it and it probably died someplace, poor thing. It smashed my passenger side in front of the front wheel and did a job on the frame.

Hitting a deer is bad enough; imagine hitting an elk, or worse, a moose!!