Not a professional but have done dozens of ponds over the years, here in central MO our clay quality is usually pretty good for a good ways into the ground, where we mostly have a problem with leakage or breaking through the sealing layer is in the center or deepest part of the pond, when a owner wants to go too deep is usually where you can run into a gravel or sand layer which can be detrimental to a pond, just did one last summer where we hit some gravelly soils, we came back and sealed it off really good with a good clay, and it seems to be holding just great.
My point being, around the edge of your pond I would not be worried at all about drilling a hole for a pier, now if you were wanting to drill on down deeper at the deepest part of your pond I would advise against it. but along the edge of the pond your chances of digging down far enough to reach a porous layer are slim. jmo
Like Anthropic says, do it your way, dont let pier pressure make your decisions for you.
