Many instructional methods that focus on analytical, skill, and competency development have a single or small set of appropriate answers. Best-answer assignments are popular for largeenrollment classes because of the relative ease with which scoring and feedback can be managed at scale. However, cheating is regularly confirmed at disturbingly high levels, with commonly used contentcomparison tools unsuited to identify original authors. We present a method to enforce compulsory attribution, enhancing the integrity of best-answer assignments. The method secures compulsory attribution of digital solutions using metadata, access controls, and extensible code available in many common applications, including Microsoft Office. A unique feature that makes this method well suited to large-enrollment classes is the ability to secure and, when necessary, delete stolen work, precluding misappropriation. This method minimizes the bureaucratic burdens associated with academic dishonesty procedures. This study, grounded in routine activity theory, describes a compulsory attribution method, called StartHere, that activates perceived guardianship in the form of interpersonal technical controls and social-ties controls for offline digital assignments. In a field experiment, we collected and analyzed empirical data in the form of qualitative student comments, quantitative survey data, and actual misappropriation events. The findings reported here demonstrate efficacy of both guardianship pathways within large-enrollment classes.