I did a new waterfall with black foam etc looks great but as the pond had water in it and I didn't drain it I never got in the pond to have the overlap fall down low enough so consequently I trimmed it only having 13cm or something overlap. 6 months later the levels were dropping 5cm a day and discovered a lake under thr liner grrr. Also my water bill went up an extra £30 a month. I've learnt from that mistake but it's making the effort to either rip it all apart or can I glue/stick on a liner on the cut but and have that go down?
My guess would be dismantle and redo.
My guess would be dismantle and redo.