my box has been crushed several times, not by problematic youth, but by problematic snowplow drivers. I moved the box further off the road and mounted it to a 4x4 in concrete. Got one year under the belt now.
My postal guy said that there is no rule regarding how far off the road a mailbox must be. He said the rules are how high off the ground and is it safe to pull over. I figured that in winter they wouldn't mind being a little further off the roadway. I talk to the delivery people periodically and they have no complaints. I may move it a little further back, but have to get rid of a junky pine tree first.
Good luck to you.
As far as the police being too busy, that is BS. talk to your local politicians and tell them you vote (if you do), sometimes that will get the ball rolling. I wouldn't expect the police to pull surveillance, but they should at least take a police report each time it occurs. In the bigger picture, if the locals have to keep filling out reports for you mailbox they will get PO'd and may start looking at the people doing it to avoid doing more paperwork. More importantly, if these peoples actions escalate you will have a record of their activities (very helpful later on).