On Wed, 07 Apr 2010 18:48:37 -0700, Dan Musicant
wrote:

-snip-
I was thinking some kind of plastic, but plastic sheeting sounds like it
might work. As long as it doesn't break or crack, that is.


Good time of year to call a place that installs ponds. That black
rubber pond-liner stuff is pretty much indestructible.

Scraps might be available. A 2 foot wide strip would be useless to a
pond install, but should suit you fine.

Dig a trench- tack a strip of this stuff to a 2x4- suspend into
trench- fill trench- remove 2x4- forgettaboutit.

Jim