Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Pond leaking through the side(s)-what to look for?

My ongoing pond issue has me asking more questions now that I have had it drained for a couple of weeks. I keep pumping out the incoming ground water as I relocate to reshape the pond. This pond is approximately 25X70X4-6' in sort of a tear drop shape with the lowest proposed depth of 4' and the deepest section being 6'.
The ground water will fill the pond to about 1' at the shallow end if I don't pump it out which I have had to do each day I work on it. The pond has always leaked down to the static water table height which can vary about from maybe 6' to 1 1/2' seasonally. I plan on lining the pond and I know there is a lot of debate about lining a pond that has ground water present but my mind is made up and I am going to put the liner in with the opinion that the water in the pond will displace the ground water enough to keep the liner on the bottom. I have to questions please:
I firmly believe the pond leaks from the sides. Is there anything I can look for that would indicate where along the sides it may have been leaking?
I had catfish in this pond until today when I drained it down to mud and slogged through the section I had partitioned the pond off to the still held fish. I have several Koi that I moved to a temporary pond and gave the catfish to a friend that has a large pond to irrigate his blueberry farm with. I have read that catfish will root around which I knew but I also read that they will dig hard at an area they sense is loosing water. Can anyone confirm this theory?
Thank You
Howard

I've never heard that about the catfish.

Most I ever have seen catfish do is make a bowl for a nest. Don't they are making you loose water.