Maybe something like this?

Pond.jpg

The ground texture is unbroken - its the same under the pond. The pond is a polygon drawn in darkish blue-green-black and blended by overlay. There is an Edge Fade Inner on it with an outer opacity of 40% and an inner opacity of 100%. Not sure how to describe that in PS terms though!

EDIT: I put a blur on the sheet (layer) that contained the pond polygon, so that the ground texture details in the depths of the pond would be blurred, as if viewed through a depth of water.