The chief marketing officer, or its org-chart equivalent, may be the riskiest job in the American C-suite. A veritable who’s who of companies–Coca-Cola, Wal-Mart, Best Buy, Gap, and Verizon –have seen their CMOs depart within the past 12 months. And that’s just déjà vu all over again: For the past three years, an annual survey conducted by executive-search firm SpencerStuart has shown that the tenure for CMOs at the top-100 consumer-branded companies has averaged a scant 23 months. (By contrast, CEOs hang on to their jobs for 54 months.) Some sector averages are particularly grim: If you’re in telecommunications, you’re looking at 15 months; in the food industry, you’ve got about a year.