Snake!!!
As far as I can tell black snakes are not interested in fish.
It will be thrilled with increased visits to your pond from local
critters. Water snakes, cottonmouths and garter snakes like
fish. They are not a commonly reported problem in rec.ponds of
old and rec.ponds.moderated.

Veggie filter - how could I have forgotten! Jim, where are your
pictures. For filtering I use plants - I have goldfish and a couple
of koi in 3,300 gallons. I have a waterfall pool that I can fill with
water hyacinth and watercress in baskets. Right now the pond is full
of hornwort - I gathered a few sprigs of the hated plant (Fish and
WIldlife
and biologists) by the riverside
and it filled the pond. Great for hiding the fish from herons and
kingfishers.

The reason we say a straight vertical side is to keep raccoons out.
Also makes
it less accessible to herons. I've had raccoons and skunks come in our
backyard and we have a six foot wooden fence. They can be tricksy.

Do pine nuts float? You can add a skimmer.

Substrate algae will grow on lots of stuff. Rock is usually
discouraged because
it will gather mud and gunk and need to be cleaned out. It looks
pretty.
Usually folks with rock have to empty the pond and powerwash out the
gunk once a year. We're too lazy around there to do that! Also plants
placed
in rock are impossible to get out. (I did a bog with rock once and I
could not
weed it, it finally grew in and we had to take it out.

kathy :-)