For swing trading of 2-3 days, I use whichever of (yesterdays Low) or (yesterdays' close - 25% of ATR(20)) is the greater (for Long trades).
For medium term or longer systems, I generally use a similar mechanism with the ATR factor being larger, and/or an ATR multiple calculated from the highest high during the trade.
I am working on the same thing and finding mixed results. I am trading trends in stocks buying options as my vehicle for leverage. Parabolics are too short and even 2 ATR's can be too big... Grrrr!!! I have been looking at an initial tight stop (0.5 ATR) and then moving to 2 ATR once it's moved 2 ATR's from the THEORETICAL entry price. i.e. sometimes if it gaps above my entry I still gotta take the trade, but my risk is larger. In short, I think a combo is gonna be the right mix, but I'm open to almost any idea.