What's wrong with the standard RPG legal system: wait for a party of adventurers to show up and kill the bad guys?
....because wizards are on my lawn NOW ruining my petunias with fireballs and I WANT HIM ARRESTED IMMEDIATELY!
I like the idea of the Guilds/Acadamies policing their own... And others who may possibly drag down the reputation and standing of wizards such as rogue summoners, sorcerers and the like.
That is certainly an idea. Maybe they have a long standing deal with the mercenary guild to provide experienced muscle in such a case.
Part of the agreement could be that young wizards go down to have mock battles every couple of weeks. I mean, being randomly attacked by casters is not common, but having the warriors have at least some idea of what they are getting into if it does happen seems like a good idea.