I am playing around with the chicken wire and concrete approach. I
need something that can stand up to cold winters in addition to
adventurous kids in the summer. I am planning builing over liner and
will have to be carefull not to have any exposed chicken wire that can
puncture the liner. I recommend making a test rock before taking on
the project. I went home over lunch and took some pictures of my test
rock.

http://members.cox.net/bokowski/rock.html

I have two more sides to texture... and I have spent two evenings this
week to get it to what you see (5 hours or so -- less if I wouldn't
have added so much water to the concrete). btw, the finished texture
was created with aluminum foil.

As far as troubles in the water... the rock should be well sealed with
all the painting/finishing processes I need to do to get a realistic
looking rock. Most of my research comes from companies that produce
water features for wildlife... so I will take there word for now. Of
course, my feeder goldfish "that I can't get rid" of will be the ones
with it on the line.