Ponds and Water Gardens - Ground Water

I am having a problem with my pond. My yard is all clay. Water is getting under my pond liner and the liner is floating. I have tried lining the liner with rocks to keep it down, but that is not working. Any suggestions?

Line the pond with large rocks.

Install a drainage system to remove the ground water.

Water coming in won't make the liner float. That is small amounts of methane gas. If you have a seasonal water table high in the winter and low in the summer. During the dry times, small leaves and grass will fall in the cracks, and in the wet times, the grass and leaves rot and create the gas.

Bigger rocks won't help that much, the gas will still push the liner up in places. Is the liner really necessary?
With the clay you say you have, water loss should not be that bad.

Just a thought

Travis