Nice fish! I saw one the other day for the first time and then I went to another lfs and saw another one. And now this one, its like it just keeps poppin up. Good luck with it.
Marine bettas are very cool fish. He may be hiding in the rocks for a few weeks. They are very shy. Be prepared to offer live foods if he does not come out to eat right away. Some vitamin-enriched brine or some gut-loaded ghost shrimp will work well for the time being.