1. If they are driving on trails that are on your private property, booby trap them. This can be done with a board and some nails facing upward, or as someone else said by diging a hole and covering it with a tarp and some leaves.

2. If you really want to use a camera, the new primos blackout supposedly makes no flash. I have no experience with that model, but I do have the primos truthcam 60 and I am very happy with it. There is also a lockbox that is designed specifically for these cameras that you can buy for about $35 that is pretty heavy duty. I use three 4'' screws to fasten it to a tree, then wrap a chain around the tree and through the pad lock which closes the lockbox. Put that about 10 feet up in a tree pointed at an angle downward toward the trail. You can leave the camera 15 feet off the trail and it will still be effective.

3. If you have the money, you can hire a lawyer and sue the DNR with what is called a writ of mandamus. If you are successful you won't win money, but the court will issue an order requiring the government agency to do their job.