Metal water pipes that are buried in the ground are also good to ground to. Iron well casings are super ground rods. Drill and tap a hole in the casing to get a good bolted connection. Connections made in or near the ground are prone to corrosion, so use proper bronze or copper connectors. Your ground system is only as good as its weakest electrical connections.
Several pieces radiating outward is best.
Try to bury them in areas that tend to be moist. If you are in a lightning-prone area, bury several hundred feet if you can. The idea is to make as much electrical contact with the earth as you can, over the broadest area feasible, preferably contacting moist soil. If you need to run any power wiring over a distance of 30 feet or more, and are in a high-lightning, dry or rocky area, run the wires in metal conduit and bond the conduit to your grounding system. Be sure to bolt your ground wires solidly to the metal so it will not come loose, and inspect it periodically.