Good stuff Glen, you and I have parallel career paths. Your concept of SPG is correct. The only way to have all the cables at 0-volt potential is all are bonded together as close together as possible outside as NFPA/NEC requires to form a Ground Plane. Now allow me to bring back memories of the PANI Ground Buss. Remember them? I bet you do. This is the best way to implement a True SPG or as close as possible. Those letters PANI are an acronym for Producers, Absorbers, Non Producers, and Isolated. It would be a ground bar literately sectioned off in 4 quadrants from left to right and the letters with lines denoting the section. This tells you how to land ground conductors. Start with the Absorbers which are your Ground Electrodes sources you want to sink fault current to. So everything you have as an electrode goes in the A Section in the middle of the Buss Bar. Next up is the P or Producer section on one side of the bar all by its lonesome self. That is where you put all circuit wires that can Produce a Surge event. That would be things like Surge Arrestor Ground Points. coax cable shields, Telco surge protector, AC Ground Bus, CATV Shields, Coax ADU, or anything that can produce an surge event. So we have Producers and Absorbers segregated occupying half the Ground Bar. That is the section of Ground Bar where outside currents can flow between each other. A Producer looking for a place to go and see the Absorber to sink the current to EARTH below. That leave you half of the Ground Bar forming an Equipotential Ground Plane free of current and voltage. I am also certain you know an Equipotential Ground Plane has no resistance or voltage between any 2 points on the Plane. The Equipotential Ground Plane is where AC and RF merge together making it SPG as good as you can make it. Now go look at the drawings I made in a few threads. Shows you that same method of madness PANI concept employs. Just simple logical solutions, proven to work, documented, and used for decades. It works and works real good. Its the best protection you can create short of going underground or cement vault.