Seems the solution(s) is cheap and easy. Only reason not to protect the glass seems to be laziness, imho. So i suppose if you are like me, cheap and lazy, it is a way to find out which you are more of. Turns out i am cheaper than i am lazy, but it is a close race.
Of course, distance and road traffic matter. You may get More hits from rocks you kick up yourself, but those coming from other traffic hit harder. They almost always seem to chip or break something. If taking shirt trips on rural blacktop, you may not catch too many.