"Easier to guard in some ways," Snape replied pensively, "but every window's as bad as a door if they simply opt for a broom-mounted attack next time. And then there's the non-trivial exercise of uprooting several research labs," including my own, he didn't add aloud. "Consider withdrawing into the underground levels: dungeons, kitchens, cellars, storerooms. Much more restricted access. And it's not a move they'd expect: us making our stand in domains reserved for Hufflepuffs ...and Slytherins."