If you really want to trap someone into working for you forever, pay them way more than they could make anywhere else. The goodwill and loyalty that engenders are really only minor components in keeping the person on-board; since people tend to spend (and get debt based on) however much money they make, you're essentially buying lock-in and making it so even if they want to quit and get an analogous position at a competitor, they probably won't be able to afford to do so.