I wish I could tell you the secret we used, but there really wasn't one. What was amazing to me is that Anna determined to quit almost entirely on her own. We used the 'ole duct tape method for a week or so, and it seemed to be working. Then Anna got sick and needed all the comfort & support she could get - and the thumb provides all that and more. So we were back to square one.
We've always promised her a reward trip to Chuck E. Cheese if she ever stopped. We've been dangling that in front of her for over a year now, but she never showed any interest in giving up the opposable appendage. Then, after she got over her illness, she asked Anita to put her blanky up in the attic because it made her want to suck her thumb. Once Anita took the blanket away, Anna's thumb never returned to the mouth. It was as simple as that.
We used this chart from the Chuck E. Cheese website... you can print your own as an incentive for other things such as potty training, clean rooms, teeth brushing and more.
So congratulations Anna - here's to going cold turkey in less than a month!