Northern Trail Outfitters wants a data model in Marketing Cloud which will prevent them from...

The best way to prevent duplicate records in Marketing Cloud is to strategically control the Contact Key values and tie records together across channels using this key. The Contact Key is a unique identifier for each contact in Marketing Cloud, and it can be set by the admin or automatically generated by Marketing Cloud. If the same Contact Key is used for a contact in both email and mobile push channels, then the contact will be unified and not duplicated.