It's already in a contract before the relationship ever starts - namely, the university/company's sexual harassment policy, most of which prohibit relationships

It's already in a contract before the relationship ever starts - namely, the university/company's sexual harassment policy, most of which prohibit relationships like this one, for exactly this reason. And such contractual bindings are becoming more widespread, because to not explicitly ban power-differential relationships in the workplace (including teacher-student) opens the organization to lawsuits.