Liner leak

Question:

I built a fish pond last year. The book I bought said to cut a hole in the liner under the waterfall liner, and let the waterfall liner hang over it. The waterfall liner kept floating to the top, so I cut it back, now I have a slow leak where the pump pipe enters under the liner. Do you have a product I can use to seal this leak? I used aquarium seal, but the fish pick at it and end up removing it. I am in South Dakota, so we do get rather cold winters. Any help would be appreciated. Paul.