We have a thumb sucker too, and I'm storing up the nail biting solution idea for some time soon, going to paint his thumb when he's gone to sleep so that it tastes horrible, nasty mummy.
My SIL however has 2 DD's both who had dummy's she cut a great big hole in the end of her eldest's dummy and told her that cause it was broken she couldn't have any more - she's 8 now and teases her mum about breaking her dummy when she was little.