Quote from NoDoji:
I normally play a breakout through a high or low of the day by entering via a limit order a tick or two ahead of the test. Yesterday for some reason I placed a sell stop at .59 and saw price fall to what I thought was 12 ticks in my favor. I put in a 10-tick stop @ .57 and saw that the level was not profitable. WTF, I thought, checked my blotter and saw the .51 fill. Never again.
<i>"As God is my witness, as God is my witness, they're not going to cheat me! I'm going to live through this, and when it's all over, I'll never be slippag-ed again - no, nor any of my folks at the CL thread! If I have to lie, steal, cheat, or kill, as God is my witness, I'll never be cheated again of my God-given ticks!"</i>
Gotta love Southern women, ya'all

If you want to err on the side of caution, you may want to use stop-limit orders - with say a 2-3 ticks allowance (maybe I just should stop giving unasked-for advice, shut TFU and actually put on my trades when I see them... but I mean well, though, peace
)