Might be a good idea to get one of the detectors that warn of potentially dangerous conditions if all else (GFCI) fails....
http://www.shockalert.com/order-shock-alert/
http://www.docklifeguard.org
https://shockalarm.com
Though any of the above will detect an unsafe condition, if the unsafe condition triggers
while someone is already nearby in the water, then it's too late. Would be good to keep people away from an unsafe condition or at least confirm safe before entering water.