NB post - most people missing the point and completely over-complicating the matter. And I don't buy the 'trailing 20%' rule either. What if the instrument is geared 10x? You will only tolerate a 2% adverse move. If it's geared 3x, you will tolerate a 6% move. Why would your tolerance for a move on the underlying change depending on the gearing of an instrument? The correct way (IMO) to handle the additional risk of a highly geared instrument is through position sizing, not through a tighter stop. If you want to reduce risk, reduce position size, not stop level. You fix your acceptable loss as a percentage of your trading capital, and then adjust your position size to match this based on your stop level and gearing. The stop level is the level at which you are prepared to accept that you are wrong, not some arbitrary move against you. The fail-safes should be in your money-management rules - eg, no more than x% at risk at any time, no more than Y% loss in a single month.
The stop-loss answer is now easy - we chart the underlying, so we set our stops on the underlying. So we set alerts on the underlying at our stop level. And when the alert goes off we go into the market to find out what is happening and to close the position at the best price we can. Over the phone or online. Simple.