Throwing rocks from bridges over roads

and trying to hit cars is apparently the new "sport" among the young and, presumably, bored. There is a piece in this morning's paper about this but of course the perpetrators won't read it.
I was dumping yet another load of street tree leaves in the bin when someone pulled up  yesterday. He got out, locked the car and then stood there leaning against his car. He looked very pale and distressed.
I waited for a short while but, as he was only three or so metres from where I was standing  I asked,
    "Are you okay? Do you need some help?"
I know, strange male. It isn't the sort of thing you should do perhaps but if someone does need help or he was about to fall over I thought it better to ask. 
   "I'll be okay but it was damn close," he said, "Take a look at the front." 
I looked. There was a fresh dent in it. It was a small dent with a bit of paint gone.
   "Little sods throwing rocks."
I understood what he meant. The rock was probably not that big  but  it could still have done a lot more damage.
There is a problem on unsealed Downunder roads - of which there are still many. The loose stones on those have been the cause of many a smashed windscreen. It is a hazard of rural driving in this country. Accidents have been caused this way and will probably go on being caused this way.
But, it should not be happening on urban "freeways" or "highways".
Designing bridges to stop it from happening is expensive. How long before there is another serious accident here? How long before someone is killed?
The stranger said all these things to me. We agreed that the thrill seekers doing that sort of thing were almost certainly bored, lacking in supervision, and unable to entertain themselves in any useful way. We agreed that, while criminal behaviour, writing graffiti was relatively harmless compared with the potential dangers and damage done by rock throwers. 
What can be done about it? I don't know. Of course you can try and design bridges to make that sort of behaviour impossible. You could set such severe punishments that at least a tiny fraction of would be perpetrators thought twice. You could hold parents responsible in some cases but what good would that do? 
All the suggestions about providing the perpetrators with "more to do" don't seem to help. The problem there is all too often that the "more to do" activities are adult directed and sport oriented. Youth workers are not generally available early on Sunday mornings and sport isn't normally played at those times, nor is it played late at night. 
     "It's going to cost a bit to fix," the stranger told me gloomily. He was starting to look a little better.
I agreed. I don't know much about car repairs but I do know they can be very expensive. There is also the time and the inconvenience involved.
He sighed and then said,
     "Thanks for the sympathy."
I watched him go off into the little "court" opposite us where there are a number of units at the far end. He was using crutches. I doubt anyone would have grumbled if he had used one of the spare parking spots in the court but he wasn't going to break the rules by parking there. 
The "little sods" could learn a thing or two from him.