bbjr RULES !!!
I just got back from the pond project. First job was to tune up the wiring per bbjr's instruction. I completely separated all the grounds from the neutrals in all downstream boxes. That did the trick! Thanks bbjr.
So...this is just one more reason to always have a separate continuous ground all the way back to the main panel. Whether it's metal conduit or a 4th wire, now it makes even better sense.
Oh, and btw, I did hook up the downstream ground rod at the second box, but only to the grounds collected on the segregated grounding bar that I installed. No prob's; worked fine.