I am going to expand my pond a bit, basically adding a few feet each way and adding planting shelves to the existing hole. I have a new liner for the new pond but was also thinking about adding a bog garden to backside of the pond. I don't want to take away from fish space so I was wondering if it would be possible to use my existing liner to build the bog and do as suggested when adding a waterfall and let the existing ponds liner (used to line the bog) drape over the side of the pond. The pond length will be about 8 feet and I was thinking of making the bog area around 5 feet long, 2.5 feet wide and about 18 inches average deep with varying depth. This would leave me with pleanty of overhang to drape over the side of the pond. In my daydream plans I'm planning on using a small lip to hold in med. sized pebble and some larger rocks as a barrier from the bog to the main pond. I have heavy red clay soil that I use for my waterlilies and they do well, without the soil clouding the pond. Would I be able to use this red clay soil for the bog or would you recommend another kind of heavy topsoil? I realize there will be some runoff into the pond water but I would like this minimized.

Is this possible at all? Would the water somehow come up under the added liner overlapping into the main pond or should I add tape?

Thanks y'all for your help.