Keep important stuff like completed account forms, log books, and disks locked in a lockable cabinet. Be sure to lock the book cabinet, and the filing cabinet, when you leave the area. (I prefer to keep them locked all the time, opening them as I need access. That way I don't have to remember to check them before I take off for someplace. This turns out to be especially useful for those times when I accept somebody else's panic and leave without checking things!)
Yes it's a bit of a pain, but it's a whole lot better than (for instance) losing a bunch of books we're in no position to replace.