Trespassing or not trespassing

We've got some family land in N. LA that backs up to the Red River. The duck hunting is good and there are several people that hunt out of boats all up and doe the river. We have spent time and money to have the kind of duck habitat necessary to make our place great, but one huge problem: the public land hunters.

Our biggest issue is a blind built on a small pond "oxbow" technically
Connecting to anther and another then to the river about 60 yards from a field in which we hunt. These guys have been asked to leave and won't. We had the sheriffs dept come out and talk to them. The sheriffs dept and game wardens admittedly do not know if this falls under the "navigable waterway" stuff, which would clear these fools, OR if it counts as illegal due to the stationary blind, them wading all over, and them parking their boat and walking across my woods to get to the blind.
The sheriffs dept said they obviously can't walk across my
LAnd and to call them when I see it happen. This happens all the time, they DnT care, and it is nearly impossible to prove it.

These yahoos skyblast at everything, hunt all day, and it messes up our blinds them being that close. The sheriffs dept doesn't know what to do and neither does the game warden.
PS the guys who "own" the blind work for said sheriffs dept.

What in the hell is wrong with people that they do this even after being approached calmly and respectfully? Sheriffs dept employees no less.

Anyone have this problem? What can I do????