May I make the point that for any ground (earth) rod or rods, the resistance is in the ground itself, not the rod. So, if two rods are driven too close to each other, in theory at least, the net resistance will not be simply halved. When separated by 12", two driven rods are likely, depending on the soil's electrical properties, to be about 70% the resistance of one rod. If driven 4 feet apart, resistance may fall to perhaps 60% of a single rod- all wired in parallel, of course. This is probably reflected in Codes.
Went to Mayenne Hospital earlier this evening for a routine heart scan 'ECG'. (Strong as an ox still, got a fuss-pot lady Doctor). Result- still A1, but when they started wiring me up with all those pads, suckers and clamps, all I kept thinking about was that bloody awful Florida Electric Chair stuff you posted in GD forum, you rotten sod!!! Cholesterol was very low too- so went to MacDonalds to top-up- you can't be too carefull!
Wood work but can't!