I also use a mechanical trading system. My experience is that if one uses a mechanical trading system for entry and one more mechanical trading system to protect profits, the end result over a period of time is much better. I super-impose my trading signals with nifty futures 5 minutes close moving average crossovers. For longs, after a good up-move, I start monitoring 30 & 70 EMA (FUT 5 min close values). If 30 EMA goes below 70 EMA, I book 50% of my profits. I go right back in if 30 EMA goes above 70 EMA. This way, I book profits for part of my position, I keep the rest of my position going and am ready to re-enter with other half. MA crossovers, in my experience, give good results. Of course, this is a matter of personal preference.
For my last long, I moved out 50% of my position @4400 (july) and re-entered yesterday @4260 (august).
Vinod is doing a great job here and I appreciate his efforts.
Vineet