There's no denying that traditional retailers are in trouble. Fortunately for stock investors, it just got even easier to bet on their demise. ProShares, a provider of exchange-traded funds, just unveiled the Decline of the Retail Store ETF. a product designed to return the inverse of a brick-and-mortar store index. In other words, the price of the fund will rise when the underlying gauge falls. This allows investors to make a short wager of sorts on the entire industry by simply buying the ETF.