@BarbO GBH land next to the pond and walk up to it and will wade into it. They are solitary but are smart and will eventually figure out a decoy is not a real bird.
As was said either nets held up a few feet high over the pond so the herons can't stab the fish through it will work. Water scarecrows sort of work but if your pond is large it is hard to protect it completely with one, water spray needs to hit the heron to scare it off.
Stringing fish line up around the pond edges can work if you do it right.
Years ago I used to have the koi addiction that others on here have, but herons have tempered it with their population control in my pond.
I still have koi, orfes, shubunkins, comets and some channel catfish in the pond, but none are that big. Shubunkins are cool looking fish all mine are runts though as they seem to fall prey to various wildlife in and around my pond before too long.
@Gemma, those are some nice looking shubunkins, big too. I have some at the moment in a 300 gallon stock tank with a net over it. I am thinking of trying to grow them larger in there then reintroduce them to the main pond.Shubs are probably my favorite pond fish.