Sorry for the late reply. I don't have internet at the house (dial up does not count).
The buried wire is about 4'. I ran it in the same ditch as the geothermal pipes.
Technically, it might work to use the ground wire for neutral, but that is a rule that I don't want to break. And you couldn't use a GFI outlet if you do this. If you put a ground rod at the end of the run (by the dock) you would have the potential for a very bad ground loop situation, because the other end of the wire is already grounded at the panel. Believe me, before I came up with the transformer idea, all of this crossed my mind. There are just too many dangerous problems associated with using ground as neutral.
