Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of equipment rental specialist United Rentals (NYSE: URI) popped 14% today after its quarterly results and full-year outlook topped Wall Street expectations.

So what: United Rentals' impressive results -- its third-quarter profit nearly tripled on 18% revenue growth -- seem to be reinforcing the notion that rental equipment stocks are becoming an increasingly effective way to play defense. In fact, close competitors H&E Equipment Services (Nasdaq: HEES) and RSC Holdings (NYSE: RRR) are also rallying nicely on today's news.

Now what: For the full year, management raised its rental-rate forecast and now sees gross rental purchases of roughly $775 million (versus its prior guidance of $665 million). Looking further out, CEO Mike Kneeland said the company doesn't see any signs of a slowdown and expects 2012 to top or, at worst, equal 2011. As long as the economy remains sluggish and customers continue to favor renting over buying, United Rentals seems like a decent place to be.

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