NEW YORK ( ETF Expert) -- With S&P 500 stocks approaching all-time highs daily, it may be more instructive to look at potential hedges and "diversifiers."Here are three ETFs that are less likely to receive accolades when investors are smitten with Google ( GOOG) and Gilead ( GILD) . 1. iShares Silver Trust ( SLV). Over the last year, SLV has served as a fine diversification vehicle due to its low correlation (0.38) with the S&P 500 SPDR Trust ( SPY). And over the last six months, SLV has been an admirable hedge against a stock market decline (-0.50). Ye,t there's one statistical relationship that may make silver a solid longer-term investment... its 10-year .92 correlation with the national debt. In other words, as long as the national debt increases, so should the price of silver. Many people believe that the U.S. will never be able to pay down the national debt, that we can only push back the day reckoning. They argue that electronic money printing and/or quantitative easing merely allows the U.S. government to borrow inexpensively until a catastrophic event (e.g., war, hyperinflation, European-style debt crisis, civil unrest, crash, default, etc.) restructures the entire economy. It's hard to argue that our national debt will go down over the next 10 years. It follows that -- end of days or no end of days -- correlation data demonstrate silver's precious nature in a rising debt environment. Equally compelling, SLV has remarkable support at a price point of $25.