Reddit reviews EasyPro Pond Products LPK EPDM Rubber Liner Repair Kit

Well, since it's a rubber (I assume 45mm EPDM rubber) then the patching is pretty easy. Most likely the cut / hole will be obvious.

But you will have to remove the rock. Just get a Patch Kit (something like this) and start removing the rock all around the edge.

When you find the cut, clean it thorougly and let dry. Make sure the day is warm and dry as you don't want it to be wet or too cold. Scuff up the liner, smear the glue, let it sit for a few seconds to tack up, and then smash that puppy on there. Rull it thoroughly and let it sit for ... I really forget. I believe it was like 30minutes. I could be wrong.

The patch will be stronger than the liner.

PVC liner is safe for fish, but not recommended, AFAIK, by people in the pond industry. PVC isn't easy to patch, and every patch I've used for PVC (RV roofs) isn't safe for fish. Personally, in my experience it is always and only the 45mm EPDM pond liner. Mainly because it's amazingly tough and resistant to tearing, and it's really easy to repair. However, for both of these it is highly recommended to use an underlayment. I cannot imagine anyone arguing that not using a substrate or underlayment is a good idea, because that's just dumb. You want to do your utmost to keep that liner in good condition. When cleaning it you are going to be walking on it and one stray sharp rock or root will puncture your liner. It's really easy to put carpet or geotextile or playsand to thwart this. I recommend geotextile.

The first question I have, is where do you live? How cold does it get in the winter? FYI, for ponds in Albuquerque, NM it is recommended to have your pond be at least 3ft deep for the winter and fish preservation. 4ft - 5ft if you have winters where the temps go below 0F for any length of time, but that really depends on how cold it actually gets.

Other than that, the size and the shelves are good. The only thing I would suggest is to put a smaller depression in the very bottom to put your pump in when removing the water and sludge from the pond. It makes it easy to get the sludge in one spot, as opposed to trying to attract it all over a flat surface. Next, the pond design should be centered around the pump location vs. the waterfall location. If you don't have a waterfall location, it'll be centered around the pump location vs. the water-out location. The water-out should be in a bog location so as to maximize plant filtration. You want water-in to be on the opposite side from water-out, so as to maximize water flow and minimize 'dead zones'.

EDIT: Apparently I typed 35mm instead of 45mm. Oops.