I currently have a 200A meter/main shut-off enclosure on a pole that was intended to support a mobile home. It is grounded with a #4 wire and rod right below the enclosure. With the mobile home now gone and a garage built, I'd like run power from that main shut off underground 125' to feed the service panel in my new garage. I'm planning on using 4/0 4/0 2/0 AL direct burial with no-ox on the connections. My question relates to the ground. Do I run another #4 bare wire the length of the run from the original grounding rod directly to the ground buss in my new panel? Do I need to install another grounding rod right outside my service panel? And am I correct in thinking that if my neutral and ground are bonded in my main shut off, then I'd NOT bond them again in my distrobution panel? I have a well and plastic piping entering my garage. Thanks in advance.

The service neutral is grounded at the pole service and establishes grounding at that point.

From the pole to home a 4 wire is needed. You mention 3 wire URD cable, and you should use 4 wire URD cable, that will have the equipment ground from the meter/disconnect to the panel in the home.

The neutreal in the panel will need to be separated and isolated, and the equipment ground conducotr will need to connect to an equipment ground bar in the panel.

No, do not drive a ground rod at the home.

If you have any metal piping in the home it will need to be bonded to the equipment ground bar in the panel using a min of #8 copper.

Perfect! Thanks for the concise easy to follow answer.

I just noticed your name, from Maine also. At the service pole there should be at least two ground rods at least 6 feet apart, per state code. Helps with the quality of grounding.