I will try my best to decribe my delimma so please bear with me.

My wife and I bought our first house last Nov and it has a koi pond in the backyard. During one of the many hard freezes that we had this winter, a tree limb snapped off and stabbed throught the bottom of the liner. It was so dry rotted that it cracked and tore away from the edges.

The former owners built it themselved and didn't leave me with an easy way to replace the liner because the just tucked it under the flagstone patio on one side and under the stone waterfall. Replacing the liner on the patio side was easy, but the waterfall side was difficult and I don't think I have done it properly.

I pulled up the stones on the patio and just mortared the liner back under the patio like it was before. On the waterfall side I took a piece of 1/2" PVC pipe and rolled the edge of the liner around it and used little screws and some adhesive to attach it. I then took some two foot pieces of re-bar and bent them into long stakes with a torch. I dug into the sand under the stone waterfall and bent the liner rolled around the PVC into the void under the lip of the stone. I anchored it with the large stakes and then used some caulk to make it water tight around the stakes. My friend that helped me suggested that we used rubber mortar to fill the void between the top of the PVC and the bottom of the stone, but it just so happens to disolve in water. What can I put between the rubber liner wrapped arund the pvc and the bottom of the stone to make a water tight edge?