Another method (which I don't use, but have heard good results with) is to place your stop above/below the high/low of the last "x" period. Traders who use this method seem to favour 4 days, but 5 days would make more sense to me as there are 5 trading days in a week. Therefore, using this method, if you were long you would have your stop below the lowest low of the last 4 (5) days. What I don't like about this method is that it can leave a lot of risk on the table in quickly advancing markets; however it does let you ride a market for a very long time.
Another good method (which I don't use because of the large risk amounts) is parabolics. They were developed by Welles Wilder, the same fellow responsible for RSI as well as ADX/DMI. Parabolics attempts to account for market volatility in stop placement, giving you very large stops at the beginning of a trend and tightening as the trend runs out of steam. It works good on paper, but I don't know if I could stomach putting a $5k risk position on in corn because that's where the Parabolic is.
A stop is your parachute. No stop, regardless of the method, will keep you in a choppy market, and I would argue that it shouldn't attempt to. Tom was famous (or notorious) for taking several small losses before hitting a bigger move. The logic? The market wasn't behaving, and since capital preservation is paramount, a small loss was more desirable than a big one.
Regardless of the stop trailing technique you use it is important to remember that the sole purpose of a stop is to get you out of a market that is not behaving as it should. NEVER trade without a stop. There aren't many absolutes in this business, but that is certainly one of them.
Erich