Pond Boss Forums POND CONSTRUCTION Soil questions Gravel Layer Below Clay Bed: Help Needed

I am having a dug and dammed pond excavated and the topsoil has been stripped. We have found gravel at various depths below a workable clay cap, the shallowest being 2-1/2 feet down, have not reached it in other areas. The comment is often made that 1 ft of good clay will be enough to seal a pond at 10' and we are not planning on going more than 8 or 9. My questions are

If we are careful about leaving a good 1' layer of clay and compact it with a sheep's foot roller, are we safe? Anything else we should be doing, or can do to ensure a good seal?

Thought this could be an issue in some of the core trench area. They ran a test hole 50' out and the gravel went down a ways. We dug about 10-12' down in one area and more gravel, but that area had 5' of clay. In the end they were able to get to clay through the 4' deep core trench. Don't know if there is gravel below but hope any gravel below will not be an issue. Good or bad assumption?

Any input would be appreciated.