All this ground rod business reminds me of a "local ground" horror story. When I lived in Michigan, the local codes stipulated an unattached garage must have a local ground (not sure if this is the case everywhere), but definitely relevant to our discussions!
This resident had ~$400 electric bills all the time, even when mild usage was occurring. A quick check of his panel with a clamp-on current meter revealed a 40A "garage" breaker which had around 35A of load on one leg. Upon investigation of the unattached garage, it was found to be largely empty and had nothing capable of that kind of load. There was a small 40A subpanel installed, with only 3 breakers in it, one for lights and 2 for outlets. A deeper inspection revealed the original contractor had made quite a few significant errors:
1. They had ran plastic conduit from the house main panel to the garage but had only included three #8 wires, all black in color, with no ends taped. (violation)
2. There was no separate ground conductor installed in violation of code.
3. The subpanel had it's bonding screw installed, which is not permitted for subpanels.
4. The neutral and one of the hots feeding the panel were swapped, such that the L1 hot was connected to the neutral bar and the neutral fed one leg of the panel. This energized the panel and ground rod with 120V relative to the "true" ground. (and the house)
The breakers were installed such that 2 were on the L1 buss bar (connected to neutral), one for lights, and one for the outlets, of which the garage door opener was connected to. The third breaker was on the L2 bar, and it was thus at 240V over the neutral bar! Luckily only unused outlets were connected to this breaker.
This discovery unveiled a giant resistor formed by the earth that was consuming over 4kw for months on end! (and probably a lot of dead worms)
Had any of the 4 errors not occurred, the problem wouldn't have existed, or would have been discovered right away.