NZDCAD just reached the 1.618 extension of it's recent abrupt fall, so I'm hedging myself until a .382 retracement of the total fall. Don't take this trade if you're not short from the top.
If price continues to fall it would be like you had closed part of your position too soon, but you won't loose money. Plus, if it does keep falling, it is very unlikely that it will never reach this point again so you can close it without loss.
But please keep part of your shorts for a month at least, it will worth it.