lodestro

Welcome to the forum.
There are two kinds of leaks.
1 a hole like in a bath tub. This is easy to see om the back side of a dam.

2 This leak is just poor soil that does not hold water.

It sounds like you may have poor soils,

Try a few thing. Get a shovel and dig a hole as deep as you can in the side of the pond between the top and the water. Fill it with water. See what it does. do this in a couple of places around the pond.

Take some of the dirt mix it with water make a ball about the size of a golf ball. Take the ball but it in a bucket of water and see if it holds together..

This will give you a little more information.

Otto