They can’t ransack the barracks prematurely if they don’t know where they are. Control the information, and you control the game.

Even if they think they have it covered, they don’t. They capture a guy and torture him to find out where the barracks are? Fine, the guy tells them — except when they get there, the barracks aren’t there. The wizard in charge of keep tabs on the gang scryed that he was going to reveal the location so he teleported the whole kit ‘n’ kaboodle to a new location.

Just make sure it all makes sense logically. If he can do that, why can’t he just teleport the PCs away? Because the barracks were heavily enchanted over a long period of time so they COULD be transported. And when you DO want the PCs to find it, the wizard can’t do it again because the PCs got there one day before the enchantment recharged.