Second Filter
I've got a few enchantments that will protect a space from magic -- hexes, jinxes, charms, dark magic in general. But it's possible that I might be able to cobble together something that will help -- but I wonder if Professor Dumbledore might be able to be of more help. He's bloody brilliant, and Flitwick's not here.
An alternative might be to cast some spells over the entrances and exits that have a sort of calming effect on people.