I had an electrician run the first two breakers from the panel, with 10 gage solid core <20 feet to my outlets, and sink a copper grounding rod, into a dirt and rock salt pool, about 8 feet between the outlets and the ground rod and use this grounding rod only for these outlets ... And yes I've had electrical engineers tell me online that this is not safe, creates a different in grounding potential, etc. however my licensed electrician was happy to do it,
This arrangement is perfectly safe provided the outlets are also grounded to the buss bar in the service panel.