Posted: 14/01/2016 at 15:53
When I had a large garden pond, the only deterrent that really, really worked was the use of Netfloats (you can find them on Google). From a distance they are all but invisible. Close up you are more aware of them, but gradually plants grow through them and minimise any visible intrusion.
They consist of a series of interlinking plastic grids which prevent the heron from getting at the fish. If they (the heron) try to step into the pond, the grid prevents them. If they try to stab at the fish, the grid prevents that, too.
After a while, the birds learn that there are easier ways of getting lunch, an b*gger off. Well - until the fledglings/young adults come a-calling. And I don't suggest that it's a cheap option if you have a large pond. But I can honestly say that it worked!
In the summer, when the heron had stopped breeding and food was more plentiful elsewhere, we had virtually no problem from their visits - and that despite being geographically located mid-way between two heronries.