The dollar has declined substantially against other currencies. To get an idea of how much it has, take a trip to Europe and bring along trunks of dollars which you can convert into a handful of Euros or Pounds. While there are some things you can do to defend your investments against a declining dollar, you should realize that it won't decline forever. And any strategies you employ will work against you when the dollar starts to rise. Also, beware of relying on the forecasts of economists about the dollar's future against foreign currencies. These forecasts are even more unreliable than stock market forecasts.
Perhaps the easiest way to take advantage of a declining dollar is to invest in foreign stocks and bonds, whose dollar-denominated prices rise when the dollar declines. The easiest way to do this is to buy international stock and bond mutual funds. Also, U.S. companies that do a lot of business overseas also benefit from a declining dollar because once the foreign profits are converted to dollars, investors benefit.
If you want to employ more sophisticated strategies to defend against a declining dollar, such as investing in currencies or commodities, you are well-advised to rely on the advice of an investment professional who is well-versed in these complex investments.