I started a thread previously on leaking waterfall, and after some trial and error, realized that the pond liner was installed discontinuously, and the top level liner ended on a stone spillway that was leaking back underneath the end of the liner (Glued down with black foam).

Below is picture with top liner removed; you can see where the liner ended upon the flat horizontal stone, in a semicircle (darker area)

I would like to repair it in a way that I'm not going to have to deal with the same leak a few years from now, so my idea is to replace the upper liner, overlapping the lower liner at the vertical portion of the waterfall, and lay the flat stones on top of the liner.

This is what the transition looks like without the flat horizontal stone, and the vertical stone below pulled back:

My question: can I just overlap the top liner with the bottom, and have it function as a "shower curtain," ie without gluing them together? Or do I need to glue/seal them together? The latter wouldn't be straightforward, you can see a fold on the left side of the lower liner on the vertical section that would be hard to bind carefully. And then there's the matter of all the gunk built up on the lower liner, whitish stuff (maybe hard water deposits?)

Thanks, this website is awesome!