It's never a bad idea to bullet-proof your stock portfolio with companies that have a clear-cut competitive advantage.
And now may be the right time to bolster your defenses with exchange-traded funds (ETFs) that buy stocks of companies with so-called "wide moats."
Of course, famed investor Warren G. Buffett originally coined the term to describe companies with distinct competitive advantages over other firms in its industry.
The Oracle of Omaha says he is always looking for "economic castles protected by unbreachable moats."
Indeed, Buffett's Berkshire Hathaway Inc. (NYSE: BRK.A, BRK.B) is chock full of wide-moat companies that consistently rake in high returns on invested capital, propelling their shares higher year after year.
The idea is to buy -- when they are cheap -- shares of companies that have dominant positions in their industries and are likely to maintain their superiority for decades, not months or years.
For example, Berkshire has held positions in The Coca Cola Co. (NYSE: KO) and Exxon Mobile Corp. (NYSE: XOM) for decades, patiently reaping the rewards from their wide moats.
"A company that has a greater duration of competitive advantage is simply worth more," Paul Larson, chief equity strategist at investment research firm Morningstar Inc. (Nasdaq: MORN) told MarketWatch.
So what gives one company a wide moat while others try to scrape by on the leftovers?
Here's what gives them the upper hand...