If wood is buried at least three feet under in wet soil with a lot of clay and sealed in, there will be anaerobic and maybe also acidic conditions. It will take a lifetime or more to rot, if even then. If you want it to rot quickly in Arkansas, leave it loosely on top of the ground in a shady and damp area and termites will quickly reduce it to nothing. For that big of a pond, I would burn and re-burn as much as possible, and lash the stumps together and sink them in the pond for cover, about two to six feet under. They will water log in a month or two.
