So I recently caught a student turning a paper that was not his with his name on it. And the only reason I caught it is because as I was reading it, it sounded too familiar. But despite being another students work and being submitted to Turnitin, it was not flagged as plagiarized. 

The student had put the entire paper in quotation marks and then simply made those quotation marks white so as to be invisible on the page. How are we supposed to prevent this?