I have to admit that installing our own Anti-Disapparation-Perimeters right after disarming the wards was a masterstroke. It was Granger's idea. Obviously. I am sure that without this precaution the Dark Lord would have disappeared long ago. Thanks to this measure, however, it will be quite a while before he finds a way to escape. I know all too well that the Death Eaters don't have Emergency Portkeys. They lack Granger's brilliance.