Greg,
I agree with the ground shift thing.
IMO, you are wasting time and materials installing Earth Electrodes any closer than about 12' apart.
One thing I have had good results with in the past, is instead of actually driving a second electrode, is clamping some stripped heavy copper wire to the electrode and burying that copper in a long thin trench at about 2' deep, this has bought down the actual earth electrode resistance and hence increased it's current-carrying capacity under fault current conditions.
