Catmandoo -- Thanks for the links! Our bubbling rock pond won't have any fish; it's mostly a "splash zone" for birds and butterflies.

Instar -- I should have said that the pump was inside of a "vault"; a large plastic box perforated with holes, so free-flowing water will seep through the gravel into the pump vault. And we plan to install the 800-pound rock in a location OTHER than directly on top of the pump vault in case we ever need to access the pump. I hope that makes a difference in your prediction of failure. :-(