Add a Requirement for a PSK in layer 2 authentication.
I have been considering this as well as it seems no matter how large a pool I create they keep getting eaten up by errant associations. The problem is that most users that will be utilizing the Guest Access wouldn't have the slightest clue as to how to set a PSK up; with all the different supplicants out there, creating a how-to document is sort of out of the question.