RichToyBox wrote:

I would beef up the deck, somewhat, with maybe double joists. The water
at 3 foot deep will weigh in at about 25 pounds per square foot, and
though the standard floor joist design is for 40 or 50 pounds per square
foot, most don't have anywhere near that.

That won't be a problem. The pond is actually at the side of the deck and
the liner will sit on the ground.

You could
also add insulation under the liner and around the sides to help keep the
pond from freezing quite as quick. Without the ground level heat, I would
suspect it will freeze deeper than most ponds.

That's definitely one of my concerns. I have no plans for fish (between the
huge numbers of herons, kingfishers, cormorants and ospreys - though I
can't imagine an osprey hitting something that small - and the lack of
power for filtration) but I don't want my lily tubers to freeze.

I think (because it will sit on the ground) that I really want to leave the
bottom uninsulated and insulate the sides. That's one of the things I'm
not completely sure of :-)
--
derek