Some thoughts.....
Post a sign saying "No Trespassing! Written permission to fish from owner is required. Violators will be prosecuted" When friends request written permission, use a generic "legal document" that includes a liability-waiver, specifies "no guests" and lists the specific date that they're allowed to fish. (Game-cam monitored at entrance). Restrict fishing to CPR, no barbed-hooks, fly-fishing only, etc, ect. "for resource-management purposes". Also include: "Times are tough. Donations toward maintenance-expenses are GLADLY accepted."
This inconvenience and monetary-jab may help reduce their visits and liberties, without making them feel singled-out.
