Two weeks ago, I committed to trying the Rhino Challenge.
Believe it or not, things have actually been going pretty well.
I've been able to stay in the 0-3 range 90% of the time, with the occasional "oopsie" snap. I think I've had one or two that might be considered the nasty snap, but I was able to calm myself down and redirect before reaching the yell. (Explanation of yells types here)
For me, just decided that "it is not okay" to yell and then vowing to report if I do, seems to be pretty effective. Committing to keep accountable by writing it up in my blog adds that layer of being watched (even if only virtually and only by the 2 or 3 people that actually read this thing), and I would never yell around most people because of the "they would think I was a horrible mom" complex.