After he reaches his destination you can set his rotation opposite of the guard position by using his lookat rotation to the target point and then reverse it.
I didn’t have time to setup a target point or anything else so I used a random reachable point in radius but instead you would use the target points location and the controlled pawn is the AI pawn.
That is a screenshot of a move to task in a behavior tree task that I setup, it should work no matter where the moveto task is whether it is run from the AI character event graph or in a BT moveto task. If you are just using the simplified MoveTo task node in the BT, then you can make a new task that will set the rotation after the move to is successful by clicking on the NewTask button at the top of the BT editor window and creating the rotate actor task.
The same way the moveto is getting it, it should still be in the black board so use a get black board value as vector and grab the key name for the target points stored vector.