I wish I could find the pictures, but I've actually seen ponds your size netted with large fishing nets. I've also seen large koi mud ponds that are netted.
I'll keep looking for some pictures to show you. I too love your scare crow
I was thinking as Tula has stated; seems you could net almost any pond as long as you can string a cable across to act like a ridge support. Then you'd pull your net(s) from one side to the other, making a tent of sorts. No doubt you'd have to sew/tie nets together to get one wide and long enough but doesn't seem any harder than all the line you're weaving right now.
Maybe just me; I tend to see solutions and try them even if they end up failing, but I can actually see this working. The trick would be to get a cable and make it secure enough so it doesn't sag too much in the middle between your supports.
@addy1 has hers on posts. Guess it depends on how much effort and $$ you want to put into this.
The other solutions are of course, a .22 (and yeah, I know it's illegal to kill herons but it isn't to scare them!) or dogs that make the pond part of their run.
Hope you find a solution so you can enjoy the pond again.