A fence should work, as GBH won't land in the water. They insist on walking from land into shallows, so a physical barrier to this will complicate their life. Also, steep shorelines help.
Last year at Kentucky Lake I watched a GBH land on the water and grab a dead fish that was floating on the surface, then take off. This happened 30 yards from the boat I was in and the fish was floating in 6 to 7ft of water. It surprised the heck out of me.
