There are various solutions to make wireless networks more secure. WPA, WEP, all sorts of encryption etc.

Well, there is one company that actually developed a physical wireless security protection!!!

EM-Sec technologies developed coating for internal surfaces of rooms that blocks electromagnetic signals. This coating creates an electromagnetic shield which makes it impossible for hackers to capture data.

I think it is a pretty interesting option which is easy to implement and that gives good results. Plus you dont have to worry whether hackers could break your wi-fi network access key.