When it comes to criminals one of the best things you can do to prevent AND combat them is having strong and reliable information networks. As they commit crimes, people will generate event/information tokens. As long as this information is being spread the risk|reward factor decreases for the criminal. You'll never be able to totally stop it, but you can make them select easier marks.
Which is a good time to mention the nuance of the guile skill tree. Lots of people (especially nobility) are nervous of anyone partaking in these skills. But these skills are excellent and major ways to collect and distribute information. So its important to not judge all actions and choices on face value, because if you keep your cool you might be able to turn an enemy into an awesome ally.
This is kind of touching on what you spoke about, with brigands guarding roads. Needless to say, life is complicated and rarely follows anyone's plans. So after recognizing that it all comes down to context, relations and enforcement. In this scenario you're now accountable for all the wrong they do. So you wanna make damn sure they're not abusing that like crazy without seeing fierce consequences on their spark.