How about browser history for a start? Go to a certain website that you know other people will not go on. For instance, say, “San Diego Zoo.” Google that, then leave it there. Chances are you brother will try and delete all history or within the day, so make sure you do a Google search of something unique before giving him the laptop. This is one way, of course he could defend himself saying he always deletes browsing history for the sake of… well I don’t know haha.