Go for it. I think what you might have heard was about cement. Obviously you are not filling the pond with uncured cement and I think that was where the problem came in. Watch I'm probably all wrong. I have used cement blocks in the pond, bricks, and patio blocks that were cement. Oh and the little retaining wall that holds the soil into my tiny bog is made with small rocks held together with cement/mortor. Don't forget that there are people out there who have cement ponds for their fish. Now somebody who knows, tell us what we've heard the warnings about.