With current yields near 0.01%, average money market funds will double your investment in 7200 years. Patience, dear saver.

So when savings accounts, certificates of deposit and government bonds also pay next-to-nothing, savers and investors have added corporate bonds as one means of boosting income. Lately, however, that's been a losing approach.

iShares iBoxx $ Investment Grade Corporate Bond Fund, the benchmark ETF which tracks high quality bonds has dropped 4.5% since hitting an early November high, significant considering the asset itself only yields roughly 4%.

Carrying credit risk, corporate and high-yield bond funds tend to track more with stocks than government debt. But the most recent decline can be attributed primarily to Europe's fiscal mess. Many "investment grade" bond funds like LQD hold debt from wobbly European banks. Over 15% of LQD's assets are allocated to European institutions, including Barclays, Deutsche Bank and Royal Bank of Scotland, which have seen their stocks plunge.

Like other fixed income instruments, corporate bonds carry interest rate risk, meaning a general rise in rates would push bond and bond fund prices lower. Duration indicates how much prices are likely to move as rates change, and the iBoxx $ Investment Grade Corporate Bond Fund currently has a duration of approximately 7.4, meaning a 1% rise in interest rates would drop the fund's price by 7.4%.

ProShares Short Investment Grade ETN (IGS) 3 months

Since its 2002 launch, LQD has attracted over $16 billion in assets, making it the 10th largest ETF and second largest bond ETF. But the one exchange-traded product that takes the other side of that trade and bets against corporate bonds--ProShares Short Investment Grade Corp ETF (IGS) --has barely been discovered. The thinly traded fund is up 3% this month but holds a mere $2 million in assets.

Bonds have enjoyed a near interrupted 30-year bull run, including a recent jump that has seen corporate bonds rally an average of 12% for the past three years. Yet a credit downgrade at home and near implosion in Europe has reminded investors that even "investment grade" assets carry risk.

IGS, which rises as corporate bonds fall, is one overlooked option that can potentially turn that risk into return.

Why go long IGS vs. simply shorting LQD? Many accounts, such as IRAs don't permit short positions. And, depending on the availability and cost to borrow shares IGS could be even cheaper to hold compared to a short position in LQD. Plus many investors simply aren't comfortable with the inherent risks of selling an asset short and prefer the limited downside of a long position.