Wait wait I've got one. We should all be happy about this decline, it's just a chance to buy more cheaper!
This knife is going right through my grubby little hands though.

Maybe just keep a stop order about 1000 dollars off the low? True you will miss the bottom by 1000 bucks but you wont buy at 8000 just to see it fall to 4000.
Which low? The lowest BTC has been since I have been involved was about $170. I don't think you mean that low however; since setting a bid a 1000 below that would be impossible. Unless the exchanges make it possible to have people disposing of their BTC by paying someone to take them off their hands.