In all the missions that you are in a camp, if your are noticed by the guards more than twice outside your hut at night, they will enter the hut you returned to and stare at you. He will then ask "What are you doing?". Wait until he turns to leave. If you do nothing, he will shut the door and lock it from the outside. However, you can either strangle him or stand in the doorway so that when he shuts it, the door will hit you and open again The guard will not notice and walk away.