Originally Posted by Judah

Keep your pedals tensioned and replace your cleats at regular intervals (according to how much riding you do), and you should be fine. I find that the only times I've unclipped were when I was riding pedals that were too loose, or clips that were getting old. It's also important to use the correct cleat for the pedal you ride, Shimano has recommendations for cleats with every pedal. Use the correct kind.