I use a cheap tarp from Lowes. I cut it into small sections (approx. 2' by 3'). Dig a very shallow hole so that the tarp will overlay about 6-8 inches. Push the dirt from the hole towards the edges, making a sort of doughnut. The edges of the "pond" should be higher than the surrounding soil. Lay the tarp in, fill with water, and pour pea gravel around the edges. Every other day, I spray mine with the jet from my hose. At the correct angle, you can spray all of the water out, then refill with clean water. I still get mosquito larvae, but they can never complete their life cycle. My box turtles love these little ponds. They're never deeper than just a couple of inches, and even juvenile turtles can climb out of them. Hatchlings, however, would drown. I harvest all of my eggs for artificial incubation, but I'll put a few pieces of flat stones in the ponds around August just in case. Any stray hatchlings should be able to grip the stone and crawl out.