NEC code has a spec for the amount of resistance
that you must shoot for, I think it was something like 8 ohms

25 ohms

If you can't get it on the first
rod, you have to
drive in a second.
....
I guess they figure if you don't get it after driving two rods, you chances
of doing better
with several is slim.

Exactly

There are other possibilities, including buried mesh screens,

1/4" 1 foot square copper plate (2 square feet counting both sides)

attaching to rebar inside the concrete of the structure.

Probably the best grounding electrode AKA a Ufer ground (H.George Ufer invented
it)

brass or copper
clamps

Bronze. May look like brass or copper at a quick glance

Usually, you
use #6 braided copper

Solid.