Board Thread:Naruto Discussions/@comment-24824859-20150112001519/@comment-1018594-20150112061607

Gaara's sand has been infused with his chakra and I'm guessing that means it only responds to him. Also, if they decide to include the fact that his mother's will is what causes the sand to protect him (they've been known to leave out important info like this), Toph won't be able to turn his own sand against him. But any sand/dirt that was there as a part of the natural landscape is fair game.