My Thought is
1) power comes in numbers and advocating for places for a legal place would have a larger impact for dirt bike riders.
2) educate the Dirt bike community on why NOT to ride the mtb trails
These are 2 powerful tools. If we utilize them then there is NO excuse for them to tresspass...then we have a right to bitch. I Know many MTBers who tresspass on land that is not designated for mtbing and specifically has signs for no biking........this is the same thought dirt bike riders have (i.e. "im not doing any harm" and "we have no place to ride")