Hi Sean,
I have stripped and re-fiberglassed the tiller on my sailboat and the
cloth was very easy to form into any shape. Then slapped on the
hardener (could be colored).
For a pond a flange could be inserted into hole cut in cloth where
needed for pipes before putting the goop on. Then I am sure some kind
of safe sealer would need to be applied that would be non-toxic.
Cement pond owners have to seal from bad stuff too.
Hope your ground does not freeze as some hard ponds have been pushed
up in deep freeze. Just some thoughts. Randy