YORK, Maine — Of Maine’s entire 3,500-mile coastline, only 12 percent is publicly held. The remaining 88 percent, which includes beaches in Kittery, York, Wells, Kennebunk and beyond, is in private hands, with rights to the beach down to the low water mark. In some cases, the town and property owners let the proverbial sleeping dog lie, and owners freely allow beachgoers to use their property.