We thought the fishing line sounded good too - then we watched the
heron
tip toe over and thru the fishing line. We then moved on to netting
the pond.
That worked, although the heron was able to stab a fish thru the net
but couldn't
extract it. The fish did survive but does carry a scar.
Now we rely on the motion detector and haven't seen a heron since it
was
installed.

Proves that it is a trial and error procedure to find out what works
for
your pond. Glad you found a solution that works!

k :-)