There's a GBH that hangs around my ponds a lot. It got almost all the small CC I was feeding and raising in my forage pond. I don't know that they can be stopped, short of netting the pond with chicken wire. If you took out one GBH, another would take its place. About a year or so ago, I came up to the ponds and a GB heron tried to fly off with about a two foot snake. It dropped the snake somewhere out in the hayfield above the ponds. I've seen a few 8-9 inch dead BG with heron strikes on their heads, and one 2.75 pound LMB with the same.