Think Sandy was just a 100-year storm that devastated New York City? Imagine one just as bad, or worse, every three years. Prominent planners and builders say now is the time to think big to shield the city's core: a 5-mile barrier blocking the entryway to New York Harbor, an archipelago of man-made islets guarding the tip of Manhattan, or something like CDM Smith engineer Larry Murphy's 1,700-foot barrier — complete with locks for passing boats and a walkway for pedestrians — at the mouth of the Arthur Kill waterway between the borough of Staten Island and New Jersey.