The heron that visited my pond stood on the pvc and kicked it around
until the fish came out. My upgrade....concrete blocks. I spray
painted 2 of them black and set them side by side. Peck-away heron.
Unfortunately this only works with some fish. Most fish swim too slow
and don't hide, therefore will be eaten. The best way to end this is
to make the pond deeper. If the water is deeper than their legs are
long they will not go in. The fish would have to swim right up to the
edge to get eaten.

Good Luck