It would be very easy to write a program that would, every week say, randomly select three bits of text from every Wikipedia page and search on that text using Google. If there were any results--well, it's hard to say how the program could tell if there were zero results--this could be posted somewhere for a human admin to check. That's the general idea. Of course, it could be tweaked, but I'll bet something like this could be made to work.

Larry