My older home is currently grounded with what looks like two lengths of old rebar driven vertically in the ground. I know that the last time the grounding was touched was over 20 years ago, and I suspect it's older than that (home was built in the '30s and additions made in the '60s).
The previous owner rewired the former knob-and-tube in the original building with Romex about 20 years back. There is the service entrance panel plus two sub-panels for the garage/apartment and laundry/porch additions. The subpanels are connected to the service entrance with wiring run through EMT but there's no dedicated equipment grounding connector in the conduit, just the EMT itself.
I've seen elsewhere that the useful life of a ground rod is only about 35 years, and that old rebar looks suspect to me anyhow. What I'm contemplating is driving two new copper-coated ground rods, at least six feet apart, at the service entrance and bonding them to the ground/neutral bus with green #6. I also thought I might drive an additional ground rod at each of the two subpanels and bond them to the subpanel ground bars (neutrals isolated outside of the service entrance). Would this be proper practice? If not, how can I improve my plan?