As mentioned, the SW corner of George Dog by Kitchen Point has very good snorkeling. There are a few NPS moorings there. If not too rough, swim around the point to the east shore opposite the small beach. I've encountered nurse sharks there and the coral is very healthy.

I've snorkeled over the Bronco Billy on the west side of George Dog, but you need to be able to free dive or scuba to get to the underwater arches.

If no surge, there is very good snorkeling at The Chimney on the west side of Great Dog. Several NPS moorings there.