No exit-method for trend traders is ever going to be completely reliable: given the multiplicity of exit-parameters available, there will always be many specific trades for which using different exit-parameters would have worked out better with hindsight.
What helps, I think, is to acknowledge this in advance, and just choose a reasonably sensible method which suits your trading-style and frequency, knowing that it will often be sub-optimal.
A method which I've used fairly successfully on a variety of time-frames is to exit a trend-following trade when the price crosses a 20-period Kijun Sen line (from the Ichimoku Kinko Hyo indicator-set) displaced 3 periods to the right - in other words, when the price crosses a horizontal line at the level of wherever the Kijun Sen line was, 3 bars/candles earlier.
It sounds a little complicated, perhaps, but it seems to work pretty well, overall, as simple exit rules go.