Six years ago Alfred Haller, a biology teacher at South Portland (Me.) High, allowed his wife Martha to try out his skin-diving equipment. "From now on, it's mine," announced Mrs. Haller, exercising a prerogative of the modern wife. Since then, for fun and occasional profit, the Hallers have dived together regularly. They hunt for sunken outboard motors or cabin cruisers, make seaweed and lobster surveys and sometimes catch their dinner. Mrs. Haller, in fact, has become so proficient under water that the Northeast Council of Skin Diving Clubs has awarded her a certificate—first class, an honor usually reserved for male divers. The Hallers' 4-year-old daughter, Crystal, is another potential certificate holder, though she doesn't yet use air tanks or weights. What is it like 100 feet below the surface? "It's out of this world," insists Martha Haller, "and I love it."