The earth ground for our circa 1968 outdoor electrical panel in California is apparently a single maybe 8 gauge(?) solid copper wire running from a capped galvanized pipe driven into the ground (50+ years ago).
It runs from the pipe into the nearby wood in-outer-wall enclosure that holds the electrical panel, then vertically up through the top of that wood enclosure off to parts unknown within the garage and house. A same-sized horizontal solid copper wire is soldered to that ground wire; the other end is connected via split-bolt to a same-gauge copper wire coming out of one of the metal electrical box's knockouts along with cable (Romex?) with that copper wire seemingly bonded to the square D metal electrical box via the cable clamp, but continuing inside the box.
Recently I noticed that the stepped diamond-style clamp on the galvanized grounding pipe was corroded almost all the way through, so I will be replacing that with a new bronze clamp.
However, I will also be driving three 8 foot grounding rods nearby, connected with 4 gauge solid copper wire, and run to the electrical box's ground connection (I have not yet opened the box's front cover; it is a split-bus style panel). My city requires that buried rod grounding systems have a protective enclosure over the top of each rod to protect it and allow for inspection. My question, however, is how to run the 4 gauge copper connecting the rods. I would like to just have it exit the bottom of each flush-buried 8-inch-deep "flowerpot" style enclosure, and run bare (no conduit) underground about 12 inches down, perhaps with a green/white ribbon buried a few inches above it to warn future excavators. Running bare would improve contact with the earth, but is it safe enough?
Photos for background info - not directly relevant to my question.