When you're just getting started with your investing, you have everything to gain and almost nothing to lose in saving for retirement. But near the end of a long career, when you start getting close to the goals you set out for yourself decades before, you'll realize that the tables have turned. Suddenly, you'll notice that at that moment, you have a lot to lose -- especially if your investments don't perform the way you want them to.

Precisely because you have more money in your late 50s and early 60s, many consider your last decade of work the most important time period when saving for retirement. What happens to your investments during that time can make a huge difference in whether you reach the finish line you've set for yourself. But even though you can't predict what kind of market you'll run into during the home stretch of your career, you can take steps to make sure that you'll be able to handle whatever comes your way.

Finishing strong
The last two decades have been like day and night for investors nearing retirement. During the 1990s, aging workers approaching retirement got a nice tailwind from a soaring stock market. In that decade, the S&P 500 more than quadrupled in price, not even including the dividends its stocks paid along the way. With those kinds of returns, it didn't take much of a nest egg to be a millionaire at the end -- not even considering the money you would've been continuing to add toward your retirement.

In contrast, the period since the beginning of 2000 has been a sobering experience even for the most patient long-term investors. Despite the market's huge recovery since the 2009 lows, the S&P 500 is still well below where it started 2000. And even when you add in dividends, total returns on large-cap stocks are just barely positive. That hasn't helped those nearing retirement one bit, although returns on the bond portions of their portfolios have been somewhat better.

Obviously, you won't know which market you'll have until you get there. But there's one way you can make sure you'll be OK no matter what happens: Take control of your retirement plan, both in how much you save and in how you invest it.

How to fix it
Taking control of your retirement empowers you to consider a number of options. If you're uncomfortable with the impact that the last 10 years of your career may have on your retirement prospects, here are some things you can do about it:

  • Change the rules. Financial plans make simplistic assumptions about how much you'll save over time. But if you save a little more during good years and let yourself cut back during bad ones, you'll likely find that the good years will outnumber the bad ones, and you'll end up having saved more over time.
  • Invest for your time horizon. Similarly, financial plans often assume that you'll earn a flat return throughout your career. But as you get closer to your goals, your portfolio should adapt. For instance, if you're an ETF investor, Vanguard Emerging Markets Stock (NYSE: VWO) and iShares Russell 2000 (NYSE: IWM) are the sort of aggressive investments you should own early in your career. Later, combining the dividend blue chip ETF Vanguard Dividend Appreciation (NYSE: VIG) with the inflation-fighting bond fund iShares Barclays TIPS Bond (NYSE: TIP) will tone down the risk level.
  • Lock in certainty. There's always uncertainty in investing, but you can control certain things. For instance, for all that high-yield bond funds iShares iBoxx High-Yield Corporate (NYSE: HYG) and SPDR Barclays High-Yield Bond (NYSE: JNK) offer, they don't give you price stability. Even the ultra-"safe" iShares Barclays 20+ Year Treasury ETF (NYSE: TLT) has lost nearly 15% since last August. In contrast, if you avoid ETFs and funds, and instead buy actual bonds from the issuer (or through a broker), you can always hold them until maturity and get all your money back.
  • Be flexible on timing. Finally, don't plan a fixed retirement date. If the markets are kind, you may get an extra year or two in retirement; if you run into a lost decade, you'll need to work a while longer. Either way, though, it's a lot easier to plan in advance for that flexibility than to deal with crushed expectations on the spur of the moment.

Don't despair
Investing for retirement may seem like an impossible task, but it doesn't have to be. Dealing with uncertainty is tough but doable. All you need is the confidence to handle changing conditions that you'll inevitably face. It's good practice for your post-career life and all the new opportunities you'll have.

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Fool contributor Dan Caplinger knows nothing's a sure thing, but he's still confident. He owns shares of the two Vanguard ETFs mentioned in this article as well as iShares Russell 2000. Motley Fool Alpha has opened a short position on iShares Russell 2000 Index. The Fool owns shares of Vanguard Emerging Markets Stock ETF. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Fool's disclosure policy gives you the certainty you crave.