Heron tips:
- put in an electric fido fence
- netting over the pond.
- a motion activated sprinkler
- a brick flue at the bottom of the pond
to give the fish a place to hide

Monofiliment fishing line every few feet. Birds hit it while
flying and get scared (they just don't seem to see it). This
is high in the air over the pond, very easy to miss asthetically.
I've been on pond tours and not seen it at all until someone points
it out. It can be three feet apart for large birds like herons and
you don't need a grid, just one direction, from what I've seen.

And no, they don't just fly around it. They panic. Its like (poetic license
here) bumping into a ghost...