I don't use stops any more - tired of getting stop hunted. Just have lots of cushion, enter near the top/bottom of the channel, set a reasonable target and wait patiently. Currently waiting for USDJPY to drop back to 115 or so - might take a few months, but I make 60% when it does. I have enough cushion to tolerate a move to 120, will dump more money into the account if it gets close to there, then short some more on the way down.
My reading of USDJPY: it's being pushed up by the carry trade, while Bank of Japan is trying to unload its grossly excessive USD surplus and does so when the price approaches 119. Currently at 118.40. So there's a push and pull between the two, resulting in a year-long channel between 115 and 119. The Economist says the Yen is the most undervalued major currency according to trade-weighted average, predicts USDJPY will drop to 109.