So long as the water level in the lined pond stays higher than the water table the forces on the liner per square foot (pressure) should be greater than the forces on the non-pond side of the liner. This would keep the liner pushed against the earthen bottom and sloped sides. This assumes no spring like flows in the water table the would increase the forces to be higher in a particular area and that none of the liner is vertical...I'd keep the sides at a 45 slope or more level. 3 (run) to 1 (rise) slope (18° measured from horizontal) is pretty common for safety reasons.

Laying earth, sand, smooth gravel. or the like can also help.

Disclaimer: I have no experience with lined ponds...just know a bit about physics.

Will the hole be void of water when the liner is installed. It would be a real trick to do that otherwise.

Fish on!,
Noel