We used a big excavator. Not sure the model, but a huge Deere. As for the rock, it's solid limestone. We live on the Niagra Escarpement. It's this ridge that loops up and around all the way to Niagra Falls. You could be right about ripping the stone. I think it might depend on how fractured it is.

As for depth, the water table is about 1 foot above the stone. So if I do a "water table" pond, I'd have to go about 10 feet into the stone. Correct me if I'm wrong.

Thanks everyone.