In the summer of 1997 I decided to enlarge the pond with a bog area as a perimeter to the main pond. The shelf was dug 12" deep an average of 3 1/2 feet in width around three sides of the pond. After putting in a new pond liner, I laid up a barrier of flat rocks covered with a water permeable fabric. This barrier was to keep the dirt from migrating into the deep part of the pond. I topped the barrier with another layer of rock for asthetic effect (to hide the fabric from view). The next step was to back fill the bog area with dirt (1/3 each native soil, peat moss, and organic mulch.)