I used to have a big blue heron problem a couple years back, and he almost got all my fish out of the bottom pond. the fix is very simple. The big blue heron has a very large wing span, and if you hang twine high above the pond from the trees to the house or something, and cross cross the twine several times, the big blue heron will not be albe to land, and if he can't land cause you take away his runway, then he can't fish the fish out of your pond! I have done this like the Japanese, but I hung pretty sparkling plastic jewels from the cheap dollar stone, and that big bad blue heron has not been back! The twine is hung high high above my head and so the pond, so it does not look bad. You only need to string a few lines for this to be cheap but effective! (You can also tie thin strips of cloth to dangle instead of jewels and I did that for two years, then this year I switched to the jewels)