Thanks for the advice

Our family maintains a cascade which leads to a koi fish pond.

The current is strong as water hits large rocks. This was loud because of large moving rocks which then broke through heavy plastic lining (22 mil).

"Lining Complaints" notwithstanding nothing was done by the installer. Did some research, ie: plastic vs rubberizeit vs
EPDM vs spray-lining polyurea for ponds & waterscapes. We studied Pond Shield and Hecht Rubber (same as rubberizeit, I think). Undoubtedly the polyurea spray-lining coatings
reviewed better than any alternatives.
Professionals who spray-on pond lining are short in number + a fortune!. Yet soft, flexible, spray-on lining of polyurea was coating required
to seal the koi pond area 690 sq ft and attempt canceling noise.

Professional polyurea installers now about $17-$24 per sq ft, I found a DIY spray-on lining of polyurea
coating specifically for ponds at Spray-Lining and Coatings http://www.spray-lining.com/pond/ .Others were Rhino Industrial dealers. Most Rhino dealers are body shops spraying Rhino-Lining, with truck bed
liner application experience. Line-X is another spray-on bedliner but they don't sell DIY koi pond kits. Verifying specifications & MSDS at SLC, a package for this particular DIY spray-lining koi pond issues was put together with instruction. That polyurea named Seal Tite was decided on.

It was over $2 / sq ft and worked- all leaks sealed appearing permanent.

Boulders are actually coated with a soft, clear
spray-lining; fully coated of 16. The bottom of the pond is got lining in
black and the sides are grey. All is a flexible
texture but not rubber between one eighth and quarter-inch thick.A buddy helped with
cleaning, my son (16) mixed, his wife & I sprayed each section. In addition to more permanent sealing if you let their support folks advise you after reading their how to, your pond should look drop dead gorgeous.

What did you do with koi while you were repairing pond?