Stray current and stray voltage (wiki)

[blacknife]

A ground probe should pull out any induced current, as well as aiding the gfci to trip. If there is damage to the hot leg of one cord the tank will stay energized until something completes the circuit, I would much rather have a ground probe do that then my body.

Hah for the record i have no ground though it is somewhere on the list of things i should buy.