Try not to have a clearly defined edge to the fairway (at least not at ground level). If there is no edge, players will take a direct line to their errant discs. This keeps the undergrowth down around the fairway.
When there is an edge, and discs go off the fairway, players will travel up and down the clean fairway to the spot closest to their disc. Then, they'll reach out and grab it, or take as few steps as possible into the rough. The rough remains overgrown. The only way out is to toss it back out onto the fairway, with no hope of making a recovery throw.
You'll find that most people who are asked to clear a fairway envision a fairway as a road. Or, like a ball golf fairway. Almost straight, no trees in the middle, with clean edges, maybe even logs lining the sides. Dissuade them of that notion.
They'll also want to drag the cut trees just far enough to get "off" the fairway - thus creating an even more impenetrable edge to the fairway than was there before. Don't let them do that.
Actually, the places where a disc will land make a shape that is wider than it is long, for one-drive holes. Think of the area before you think of the lines.
Ask them to remove all the dead or unhealthy trees and branches, trash trees, vines, thorn bushes and invasive species. Only take enough of the healthy trees to get the equipment in there. (You might want to mark some special trees to make sure they save them.) Then take a look and see where the holes should be.