While Keeps were always intended to provide some protection against roving bands of marauders in a very hostile world, they were never intended to be 100% safe. While there are upgrades to the Keeps that allow for many different types of guards to provide some protection against intruders, as well as a debuff inside the central Keep building which prevents enemy stealth classes from entering stealth, neither of these is a 100% guaranteed deterrent. There are specific mechanics given to certain races and classes (particularly Fae and Duelists) that make it possible for them to bypass the walls of the Keeps. Those mechanics were put in to ensure that there are always dynamic gameplay opportunities: even in Keeps, there could always be danger lurking in the shadows. We recommend that when you are in a friendly Keep, you remain vigilant, and if you must AFK, the best place to do so is inside the Keep central building where it at least forces any enemies out of stealth who may have snuck inside.