Non-lethal would be stringing fishing line from stakes in areas that it likes to frequent.
Like Scot says this is a worthwhile option and is not as difficult as it sounds. You don't need that many stakes and you simply run mono from stake to stake around the pond a about 2 1/2 feet off the water. The idea is, since a heron does not land on the water like ducks and geese, but wades in, he will be frustrated and prevented from fishing in the pond. Another option is an electric fence if you like to watch a heron do a break dance.
I don't know if Wi. requires you to have a permit to permanently remove them like Indiana does.
It's not actually the state that regulates this but the feds. The bird is a federally regulated and protected bird just like other waterfowl. A permit cost $100.00 and you have to be using all nonlethal methods at your disposal first. I doubt they would give a permit to a recreational pond owner though.
I heard that they are allergic to lead when delivered at high velocities.
Just don't get caught or tell anyone if you go this route. Since it's a federally protected bird you can get fined severely.
