I kind of expected their "anti-esper measure" to be speakers that let out that one frequency used at the juvenile detention center. A: it's been shown to work and B: with several of them having the speakers it would be difficult to take them out before it messed with powers. But I guess that would lead more to an out of control esper, rather than just an aggressive one, which is potentially more dangerous (or less, if said esper is cautious).