I don't really know why you would want to kill every snake you saw near your pond. They really don't eat that much, and having them around will help control any rodent problems. Even though it may seem like they are plentiful, snakes are in decline throught North America. I can see taking them out if there are way too many, but a few snakes around your pond don't effect it too much. I am sure it would be fun watching a bass nailing a garter snake swimming across the surface of the water anyways.
