I installed my first pond a few weeks ago. Not very big, about 500 gallons or so. I learned a lot, and it turned out well. I was really worried about the liner the whole time, afrait to step on it, afraid to step on the small river rock once I put it on top of the liner. I doubled up on underlayment, but I was still worried that I would puncture it. Also, I placed a pretty heavy and large rock in the stream which hands out over the pond and the water falls off of it. I was worried, however, that I would somehow puncture the liner doing this. On here I see guys putting rocks which look like they weigh a ton, literally, right into waterfalls and on liners. How concerned should I be about this? EDIT: Also, I excavate the dirt under the liner as best I can to the shape of the rocks I want to place, but there may be 1-2 inches in some spots, and even bigger gaps in other spots where the water will run behind the rocks. Do all fo you use the expandable waterfall foam to fill these gaps and route the water?