Dori has a point of course, but do we really have this problem?
If so, then "soft closing" might be a good solution to explore. A "soft closed" wiki requires a captcha for posting, disallows external links, implements the 'nofollow' tag, etc.
Forgive my ignorance as a non geek-english speaking cloggy ........ what is captcha?
Waerth/Walter
ps) I am willing to take 2 or 3 more wikipedia's under my eye toprevent it from clutter/vandalisme so it can stay open.