I seen sulution how to stop the heron taking anything
from the pond . you simply put up some small sensor that start
a sprinkler system to sprayer warter over the pond evry time
the heron get near the pond , only thing if you want to get
near the pond yourself, rember to take of power of the sensor
..
you can se how it works on

http://www.elspaden.dk/Files/Motion%205.avi
http://www.elspaden.dk/Files/Motion%20232.avi
http://www.elspaden.dk/Files/Motion%204.avi

the link will open your windows mediaplayer

I found the movies on http://www.elspaden.dk/havedam.htm and I
am sure it will keep the heron away from your pond.
Birgitte