Blue Heron is Eating My Koi

One solution I read recently was to place chicken wire a couple of inches below the surface. The pond still looks the same, but the heron gets frustrated and goes elsewhere.

I would opt for wire or netting, too, but if you'd rather not do that then, I have heard that, if you put an ornamental heron by your pool it deters others from landing.

Chicken wire or plastic netting over top if pond is not too large.

I recently read that you can put various lengths of pvc pipe in the bottom of the pond to give the koi a safe place to hide. Just make sure the circumfrence is big enough for the koi.

Maybe you could cover the pond with some kind of netting. Fish hatcheries do that.