George,
I have a heron problem as well. I bought a crossman co2 pellet gun and at least for now they have stopped stopping by. The instructions said to fire one or two times without a pellet because these shots might be under powered. The second shot, sounded like a .22 and scared the heron off, he returned once more and opening the screen door scared him off and he has yet to return, about two weeks. I have yet to fire a pellet, but I want to.
Like Anold he'll be back. They are very, very, persistant birds if they find a honey hole.
