Re: Subpanel grounding
A ground rod will almost never be able to clear a fault. The inpedance of the earth will limit the current to a level too low to open the overcurrent protective device. When I teach a grounding class, sometimes I have them install a 10' rod in the yard. We then connect to the hot wire from a 15 or 20 amp circuit to the rod and put a amp-clamp on the wire. It has never tripped the breaker and the most current I've ever read on the meter was 7 amps and that was after 3 days of heavy rain. The grounding electrode system is only intended to help provide protection from faults outside of the system, like lightning or a high voltage line contacting the 120/240 volt lines.
I feel that the ground rod at the subpanel would better service the purpose of fault dispersal then a long EGC conducter.
"It is the first responsibility of every citizen to question authority." B Franklin