This is not a "buy and hold" short. It is for short-term trading at most. You can get into a lot of trouble with this one because of the various decays that eat away at price.
Research and understand the impact of "volatility decay" (the major decay of concern here) before you think about fooling with this. There are plenty of good articles on it on the web so I am not going to go into details.
An example problem with holding this is:
1) Buy DXD when the Dow is at 12000
2) Dow rises to 12500. You are therefore losing money.
3) Dow goes back down to 12000. You will still be losing money because of volatility decay. The Dow will have to go below 12000 for you to just break even. How much depends on the price action that took place during the whole period.
Any fund that you buy to short the market is going to be an inverse fund and will therefore have volatility decay. This fund is also leveraged so the effect is magnified.