Dear Mr. Moore,
One variation on the acrylic sheet idea is to paint on resin and brush the ripples into it as it cures. Wasco Taxidermy Supply sells a video of doing just that (as well as making really cool splashes), using polyester resin. The technique may work with more eco-friendly water-clear urethanes, also. The video is titled "Splash & Ripple Construction with Frank Newmyer" and the home page of the supplier is http://www.taxidermy.com/ . Go to "Taxidermy Videos", then "Habitat and Exhibit Construction" to find it. Sorry I don't have the exact link, their website is coded wierdly. Now all you have to do is figure out a way to reach the entire pond with a brush! Good luck with the project.
Cordially,
Paul Pallansch,
Dioramist/Sculptor,
Up-Close Realism