I found the leak, it's done. But not without weird things:
- The 1" PVC pipe I initially found that wasn't leaking turned out to be part of the sprinkler irrigation system. The 1" PVC main was directly underneath it, about 10" deeper.
- Speedy Jim was right: the leak was at the coupling/adaper between the 1" PVC pipe from the meter, to where it connects to the 3/4" copper pipe that goes into the house. This coupling was a good 15 feet away from the shut-off valve.
- Get this: the leak occurred in the PVC adapter, a 1" inch female slip fitting that reduces to a 3/4" female NPT, which screws onto the copper pipe. In the middle of the adapter, there's a 1/"-wide hex-ring molded into the fitting. The leak was a hairline fracture that spanned 3 flats of the hex-ring, but perfectly centered around the circumference. Odd, that, I think.
Anyway, after LOTS of digging, tearing up landscape timbers and brick patio, and a few swear words, the leak appears to be fixed.
Thanks heap for all replies,
-Zz