It is one thing to be tailgating the car in front, there is no excuse for that as any stones chips would be rightly deserved. If roads have poor surface areas and the driver in front keeps on driving like a cut maggot then that is what I call irresponsible driving. It doesn't matter how many car lengths you try to slow to because the damage is already done. Drivers that cut corners and run there wheels over the gravel/dirt on the side of the road should be booked, they are to lazy to steer within the lines so they just cut across, it is shameful. I've had trucks at about fifty metres still manage to spit rocks at me and to overtake you have to speed well over the limit to get past them, Truck drivers should be a little bit more wary in high traffic areas to drive slower to avoid damage to other cars, not to mention making it easier to pass them. I'm speaking mostly for semi trailer size trucks. I don't know what the roads are like over where you live but in Tasmania it is safe to say that there isn't a road that is built here to handle a large truck driving at pace.I was once stopped by a very understandably angry someone who said a stone was thrown by our rear wheel and broke his windshield. I assure you that such things both happen and are random occurrences. They are classed as "road hazards" here and are not generally actionable against the car which threw up the rocks. If the offending vehicle is a truck which drops material onto the road and trailing vehicles, that is quite another matter. But if you can drive so as to toss up gravel to damage a chosen following vehicle, then you are a much more skillful driver than I. I generaly don't even notice chunks of gravel on the road unless there are enough pieces to constitute a pile.
MIchael