After seeing the pitfalls that come with being a one-trick pony, I have to commend footwear designer and retailer Skechers (NYSE:SKX) for its success in pursuing a diversified approach to selling shoes.

The one-trick pony I'm referring to is shoe rival K-Swiss (NYSE:KSWS), which is hurting from an over-reliance on its Classic shoe brand. Classic makes up 65% of K-Swiss sales, and U.S. consumers despise the shoe right now. Skechers, on the other hand, is firing on all cylinders; it recently touted the creation of "10 on-target brands," and it's currently enjoying celebrity backing from the likes of Jessica Simpson, JoJo, the Game, and Nas. I have no idea who most of those people are or why the shoes they endorse are selling, but kids want 'em.

Skechers' reach doesn't end there: It also targets men and women in the "active, casual, dress casual and dress footwear" market segments. And it's all working; management yesterday announced 20% sales growth for 2006, while diluted earnings jumped 50%. Its first-quarter outlook was also strong and ahead of what analysts were expecting.

Shares of Skechers have almost doubled in the past year and now trade for a lofty 24 times trailing earnings. Its price-to-earnings ratio will look more reasonable if bottom-line trends continue their impressive run. Problem is, the footwear space is subject to volatile fashion changes: what's hot one season may sit on store shelves the next. K-Swiss is currently suffering as consumers shun its Classic design, while Timberland (NYSE:TBL) is an erstwhile boot brand icon. Deckers Outdoor (NASDAQ:DECK) is all over the map with its Ugg boots, and bearish investors continue to circle over highflying Crocs (NASDAQ:CROX). The list goes on and on.

Additionally, Skechers' yearly net profit margin is still only 5.9%, even with the success it is seeing selling its brands. In contrast, K-Swiss posts margins near 15%, and Deckers' hovered around 12% over the last 12 months. Again, things are going well at Skechers and could continue for awhile, but I don't see much in terms of a sustainable competitive advantage like I see at industry leader Nike (NYSE:NKE). I may also be interested in K-Swiss if its stock falls to the low $20s. You can keep the other footwear stocks.

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Fool contributor Ryan Fuhrmann is long shares of Nike but has no financial interest in any other company mentioned. Feel free to email him with feedback or to discuss any companies mentioned further. The Fool has an ironclad disclosure policy.