First, there was the sound so high pitched that only teenagers could hear it. It was put into a device that could be played in places where the tribes like to gather - shopping malls etc. - to disperse them without even realising it.
A few days ago, m'friend Simon reported that the teens have struck back by adopting it as a ringtone so that only they can hear their phones go off in class.
The Today programme this morning now reports that Sydney shopkeepers have resorted to playing Barry Manilow to move the herd on. I can pretty well guarantee this will never be used as a teenager's ringtone, but I await the next development with interest. Sooner or later it will cross that indefinable line into cruel & unusual; in fact I'd say it's nudging the line already.