Ghost, it sounds as if the 'cut the plug' question would be a very good question for "UL Corner" in the IAEI magazine. I'd love to have an "official" statement on the subject.
Greg, the issue of "equipotential plane" does not come into the picture, because the "Pool And Spa" code (yes, there is one, separate from the NEC) does not apply itself to bodies of water less than 18" deep.
Even so, I'm a bit at a loss as to what such a 'plane' could possible accomplish. Construction is entirely non-conductive; absolutely nothing is 'grounded' (as the place has but two-prong receptacles), but all is on a GFCI. Even for the pumps, no metal is in contact with water - the impellers are magnetically driven.
Now ... for the 'sales pitch' ....
... drop by the chat room! I'll be happy to share pics, and discuss my specific water garden. I'm there most every night, roughly 6PM-9PM, Pacific time.
BTW ... I wonder if electric eels trip GFCI's?