This spring I have been thinking about moats a lot. No, I am not thinking about European castles, drawbridges and siege warfare. Rather, I have been thinking about the metaphorical moats that companies need to keep competitors at bay. Given my taste for high-quality enterprises with durable competitive advantages, I am always thinking about economic moats, but two things have put the issue front and center for me lately.

Recently I attended the Berkshire Hathaway ( BRK - news - people ) annual meeting with some Ariel Investments teammates. We love to go and get an annual refresher course on value investing from the legendary Warren Buffett, whose style I consciously emulate. His answers to shareholder questions returned to the moat concept again and again while discussing Berkshire Hathaway's recent acquisition of Lubrizol ( LZ - news - people ), Berkshire's housing-related businesses and the strength of the U.S. economy.

Buffett's moat concept has been the centerpiece of his philosophy for many years. In an interview more than a decade ago he noted: "The key to investing is not assessing how much an industry is going to affect society, or how much it will grow, but rather determining the competitive advantage of any given company and, above all, the durability of that advantage. The products or services that have wide, sustainable moats around them are the ones that deliver rewards to investors."

Independent research firm Morningstar has actually trademarked the Morningstar Economic Moat, which measures the degree to which a company can sustainably protect its profits. Wide-moat stocks have the ability to withstand competition for a very long time, while no-moat companies lack meaningful competitive advantages. Morningstar acknowledges it is much easier for large companies (think Coca-Cola ( KO - news - people )) to have wide-moat ratings than it is for smaller companies (think Crocs ( CROX - news - people )). I was thrilled to see my flagship Ariel Fund as one of three small- and midcap funds singled out by Morningstar for having portfolios chock-full of companies with moats.

Like Morningstar, ( MORN - news - people ) we judge whether a firm's advantages give it a wide or narrow moat--or no moat at all--and we also consider the future. In his book Poor Charlie's Almanack (Intermountain, 2005) Charlie Munger, Buffett's right-hand man, notes that superior firms have deep moats that are continuously widening to provide enduring protection. In light of this we not only specify how wide a moat is but also how it is trending. Is the moat stable, growing or shrinking? Sometimes it pays to own companies that everyone recognizes as wide-moated, while other times it's a contrarian view on the moat that matters. Here are some examples.

I have owned McCormick & Co. ( MKC - news - people ) (MKC, 49) in my portfolios off and on for years. It's the world's largest spice company and has a remarkably strong global brand, specializing in unique spice blends, pepper grinders, soup mixes and more. Consumers equate its name with high-quality flavor. It also provides seasonings to restaurants and food manufacturers, with a list of marquee clients that includes Frito-Lay, McDonald's ( MCD - news - people ) and KFC. It has multiple customer bases and a strong moat for each of them: No shopper, restaurant or potato chip company is likely to take the risk of trading down and serving food that doesn't taste great. The stock now trades near the market multiple. Given the huge opportunities it has in emerging markets, I think it has powerful growth in its future.

One of my newer holdings is Fair Isaac Corp. (FICO, 28), creator and owner of the FICO credit-rating score. Its credit database remains world class, but a lot of people think its moat is dwindling. Competitors have created their own ratings, and credit card usage is down. I see Fair Isaac's moat as narrow but stable. Credit card use is in a temporary trough, rather than stuck in a long-term decline. Wall Street sees Fair Isaac's growth in the low single digits, but I think it will be well into the double digits. Now it sells for 14 times next year's earnings.

Meredith Corp. ( MDP - news - people ) (MDP, 30) is a media company best known for magazines like Better Homes and Gardens. The crowd, obsessed with iPads, the Internet and disruptive new media, seems to think magazines are going away. I don't. Periodicals that compete with the Web for timeliness may struggle, but those with unique content, such as FORBES and most of Meredith's lineup, have staying power. Meredith trades at a 33% discount to its overall market, and analysts expect 20% earnings growth this year.