If dump truck drops rock and breaks windshield what are your rights?

If you can prove the truck broke your windscreen then you should be able to sue him for the damage in a small claims court. However there is a problem with this coarse of action. By the time you get the money for the windscreen you will have had to go to more expense than is worth the effort in the first place.

There is actually a simpler way to go about it. You simply report it to the police - such incidents are considered to be accidents - and, if the determination was made that they were at fault, their insurance will cover it, and there's no need for the small claims court.