How to select best Earthing Electrode ?

ours are all solar powered battery backup with a 120 backup charger at the barn.
We use a normal voltmeter that we already have, we dont need a new tester. I got my VTVM for 10 bucks at an auction

Thanks for that summary, Tes. However because of the apparent requirement for good contact I had assumed that Al was looking for a building or lightning-rod ground. In the case of parallel earthings I was interested to learn what sort of max resistance reading between the two would be required for safety