The expression 'grounding ring' is a term of art.
Dig a Ufer trench but go beyond #6 bare solid -- use 1/0 stranded instead. ( Presumed 900 kCMIL aluminum feeders ... see 250.122 table. )
Come down out of your Service in PVC with a provision for a bonding lug where the GEC leaves the Service IF IT IS METAL.
If your Service is a NEMA3R pad-mount then break out the roto-hammer and punch down through the pad, tunneling down and away into your UFER trench.
Strictly speaking once you've gone beyond #6 ENCASED in concrete you are no longer installing a UFER, per se. Instead such GEC's are referred to as GROUND RINGS; and no, they don't have to loop entirely around the building.
( You could, but only the government is willing to waste that kind of money.)
I normally place the STRANDED 1/0 within clean, moist sand at the bottom of a UFER-length trench ( at least 30" of cover )and have it inspected. ( The end and the start being still exposed to view, the rest under 3" of sand and in my area the GEC must have AT LEAST 20 feet exposed from start to finish in the trench, the GEC then continues unbroken via deep burial/PVC/concrete cover up to the Service bonding rail.) Then I would normally puddle a rat-slab of concrete over it at least 4" thick. After it dries I hit it with marker paint, typically red or orange. Finally, I bury the work with clean fill starting with the remainder of the sand on hand.
At 600 Amps and without metallic piping a supplemental electrode of this size is necessary.
Further inspection of 250.53 (2002) especially in the Handbook will prove fruitful.
As it stands you have an ungrounded system and no end of troubles can come from that.
