Do you mean the halberd guard, I also have problem with him. From the door and rock throw range, I dont think there is a way to bait him to turn on the way out. Eventually, I gave up and killed all guards. If you are a mage you can use abomination staff to tentacle kill them with no penalty.
Yeah on my way out , there is that door and the guard that stares at it and I need to be careful while concentrating on that door the guard from the bellow area at time patrol upward and if you hide in the boxes the guard still can spot you and skewer you with the spear sadly enough.
So I need to toss one down bellow first.. then open the door and toss forward just a bit in front of the guard with the bucket helmet as that is diffrent from the rest, the bucket helmet I can't tell if it is a halberd or a spear, lol when he turn to get back to his position I sneak hurriedly past the dead alert point just beyond the door and then move below sadly when near the area below I kind of suck, I trigger the people to go alert but not the timer alert and I just run and make it to the door down south and exit the place.
I reload the saves and redo like 10 times, lol before I manage to escape so yeah the challenges are tough at least for me but it feel good once I get it done.
Speaking about sneaking, I need to do more sneaking at the follower of the saints place boy that was fun. LOL I totally suck on that sneaking part in the saint's place and so glad the plot storyline progress the way it is and doesn't have any severe consequences of worth to note.
lol 
