decoy fish

Jan, I noticed that you mentioned you had a "decoy" fish to scare off the
herons, and I was wondering what you (or anyone else that has one) thought
of its effectiveness. They showed me one in the pet store and I burst out
laughing when I saw how big it was! I guess the idea is that the heron
tries to grab it, realizes it's made of wood and gets frustrated and goes
away...? Does it float on top of the water? Thanks for any answers.
Kirsten