10 year ago (I am looking at the S&P index now), the index is ~1050 and today is 1320. If my math is correct, as of today, the yield is only ~2.5% compound annually, and I believe a CD can do better at no risk.

I hold SDS ETF now (only 20% of my portfolio though), and rest of the money is in CDs and money market accounts. I will hold the SDS ETF until early next year or even longer. I will also consider buying some FXF or FXY if they begin to drop by a bit. You can laugh at me next year when SDS when to 10 dollars or lower :(.