If you use a grounding probe, make sure it's plugged into a GFCI (ground fault circuit interrupter). If it's not plugged into a GFCI, your tank is more dangerous to you than without the grounding probe since YOU will be the new "ground" to any stray voltage.
Ground probe + stray voltage + no GFCI = electrocution.
Ground probe + stray voltage + GFCI = tripped breaker.