I use an intermittent electric fencer after the raccoons cleaned me out. Once the herons started visiting I found it works great with a single wire across the pond. If not hidden in your backyard check city codes.
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I have heard from others that using an imitation heron placed in or by the pond also works since herons are territorial and solitary. Haven't tried this since possums and raccoons are a bigger problem for me.
. They are beautiful birds aren't they.
Good luck and I hope you find something that works for you.