"Bob Miller" wrote
My main problem is there is solid rock/limestone about a foot down. I
can't even penetrate it with my Glen Martin ground rod driver. So
putting down a new rod probably means digging a shallow ditch and
laying it down horizontally -- or laying some radial wire, or both.

bob
k5qwg

Hi Bob, the horizontal burying of ground rod is fine, although a minimum
depth of 3' is recommended in NFPA-780. Follow the same plan as for vertical
ground rods by burying two additional (min.#4 wire) conductors for another
20' in a "Y" direction and repeating a horizontal rod at each of those
locations.

horizontal horizontal
----------- --------------
\ /
\ /
\ 20' 20' / buried #4 (min) bare
copper
\ /
\ /
\ /
\ -------------- / horizontal
|
|
|

Even in dry soil this will be a much more effective ground than a single 8'
vertical ground rod.

73,
Jack