Gents, this fort is the safest place in the verge, for some reason in the verge no matter how much one lights a place up mobs will still spawn, but thanks to a hunch of mine and a little experimentation I found out they cannot spawn on cobble, hence the interior is completely cobble flooring and walls have a lip so that spiders cannot climb them, the only risk the fort is in from critters is ghasts and it might even be to high up for them.
It is pretty well protected from players as it is located on the very steep mt Norgirn, a river provides for a natural moat, There are six separate guard towers protecting the walls, and the forest surrounding it are infested.