A word about the ETFs

From the ProShares TBT website (emphasis added):

"This ETF seeks a return of -200% of the return of an index (target) for a single day. Due to the compounding of daily returns, ProShares' returns over periods other than one day will likely differ in amount and possibly direction from the target return for the same period. Investors should monitor their ProShares holdings consistent with their strategies, as frequently as daily. For more on correlation, leverage and other risks, please read the prospectus."

As such, the strategy is a short-term strategy -- the holding period should be days, maybe weeks, but not months.