Cut the stock and barrels off an old shotgun. Fix it to a post under a hinged plate with a hole in it. From the plate attaché a rod so that it just rests on the trigger of the gun...
Place the pole in the pond (plate upward), load the gun... And await Mr herons arrival with glee...
It doesn't matter if he doesn't bring glee with him really. The result will be the same... A loud bang, a splash, ripples on the water, and a few down feathers gently drifting in the breeze.......
innit....
Not my idea, it's an old wildfowlers trick...
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