I would not use them at all. I think you are most likely to lock in losses and miss out on gains than to "protect yourself".
Can you point to any successful mutual fund that uses this strategy? Can you point to any well constructed study that shows that this approach improves total returns?
If you want to protect yourself at some point, you could buy puts. Then you know exactly what you are losing - no loss of gain outside the premium you pay. Like brewer
says, investing is all about risk/reward - if you don't like the risk in these stocks, you probably should not be buying them.
And if you think you have some simple magic formula to collect gains and stave off loses, I have a design for a perpetual motion machine to sell you
edit/add: Can you say "Flash Crash"?