Douglas Cahanin had a problem. A second-year student at The John Marshall Law School, Cahanin was realizing — as so many law school students do — that he was headed toward an uncertain future. He had already decided to distinguish himself from future competition by studying derivatives regulation when professor Michael D. Schlesinger spoke in front of Cahanin’s corporations class. The subject of the speech? John Marshall’s Business Enterprise Law Clinic, known as BELAW. This was a chance …