One thing I have noticed that has helped is when my Black Lab Sheds around the pond. His fur must be something that tells the Herons and most other animals to stay away. Or it oculd be he just needs a good bath and the stink is keeping them away!! \:\)

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1/10 - 1/4 acre pond plus 16 ft deep/ Plus 40 ft by 20 ft by 6 ft deep koi and fathead minnow pond next to it. Upstate NY