You can use anything conductive, grounded material, AFAIK, a metal mesh screen works as a Faraday Cage covering.

http://en.wikipedia.org/wiki/Faraday_cage

or, for the more paranoid:

http://www.ehow.com/how_6618709_build-faraday-cage.html

8-o WWIII ! ) . . . just half-kidding. :-/