The big guy that runs across the back does just that. Once he reaches the otherside of the screen he stops. He does not even try to come in to the walled in area. You can even go out on the road and he will not come to attack you. Walking next to him is not recomended but he appears to be afraid of you. BTW he has about 90 hit points.
The real problem with this mission is the spiders. There are theree manholes they come out of, and they pop through the floor. If you have an explosion pack you can shut down the manholes. Making it relatively easy.
If you don't have an explosion pack but you have a jetpack you can jump up on the wall and just shoot at the big guy. The spiders cannot climb. A Laser weapon will work wonders here.
You can buy THESE weapons before the mission.