A grounding probe without a GFCI device is inadequate protection. There are many fault scenarios & the best bet is a GFCI with respect to safety. By the time a 15 amp circuit breaker blows, if any of your body parts are in the tank, you will be a hurting buckaroo, if not dead. Circuit breakers are to keep your house from burning down, not for personal protection from getting shocked.
http://angel-strike.com/aquarium/GroundingProbes.html
http://angel-strike.com/aquarium/GFI...alDetails.html