kathy wrote:

Besides netting you can try electric
fencing and motion activated sprinklers.
Depends on your yard and how your
pond is situated in your yard.
Takes some experimentation!

kathy :-)
www.blogfromtheblog.com
there is an article about herons
archived under April.

Also make sure that your fish have several places to hide either create
a "cave" by placeing a piece of slate across two rocks or place large
flower pots in the water. Also some people find brightly colored fish
decoys to take the herons first strike effective.

Good luck