spacedog is correct: the work belongs to YOU, since you contracted it. What this guy's planning to do is technically illegal. If you can prove that you contracted the work, you can more than likely sue when he tries selling it. I don't know all the legalities of this particular incident though, you really need to seek a lawyer's guidance for this one.
And ummm...spacedog...relax a bit, eh? No need to be ultravulgar, there are ladies present.
