http://c2.com/cgi/wiki?MoreAboutCodes
The ideal is to post a notice above the edit window with a field where the code word must be entered.
I've given up edit access to a couple of my sites because of systematic spam abuse. The EditPass mechanism in usemod works, however, seems cumbersome and less than anonymous having to go through the preferences form.
I like the c2 wiki solution for it's simplicity.
My 2 cents. --MattOlson