Possible solutions: A good idea would be to grand them temporary guest access that gives them just an Internet connection and nothing else on your network, such as shared drives or printers.
Vendors have begun to enable this on their routers in a variety of ways. For example, an option called "Hotel-style," meaning that users are directed to a Web landing page where they enter a special guest password (For example our dormitory is also using this option for all students and guests). Other vendors make it easy to set up separate wireless networks just for guests.