I read something a while ago which suggested that windsucking could be the result of a horse trying to alleviate the symptoms of a stomach ulcer - have a google on 'tinterweb and see what you can find. I'm pretty sure there was one of the herb companies who prepared a potion for windsuckers - maybe worth a try. Otherwise, you have to remove anything they can grab hold of but of course there are some horses who don't even have to grab, they just stand there and do it.