I have looked into this a little bit more -- I just realized that the existing software does give us some tools to combat this kind of vandalism.
First, I have fixed it so that only editors can edit the HomePage. I think this is less desirable than our ideal system in which all the regulars magically and transparently have this power.
If you want to edit the homepage, email me for the administrator password -- I will give it out more or less willy-nilly to anyone who I know. If the vandal starts using the password, then we'll know it is an "inside job" and we'll have to think harder.
Second, I have added some ip numbers to the banned list. I'm prepared to add more. This is less than 100% ideal, obviously, since innocent people might be at the same ip numbers.