They could make it kind of like basketball. In basketball if you stand, or rather camp, in the area under the goal for more than a certain amount of time, you get a penalty. So, if somebody in HALO stands still in some place other than where he spawned for more than like 20 seconds or something, then he should be warped back to a random spawnpoint. That would not only end his camping, but make him vulnerable in the same way. Also, it would be a nice surprise for the camper.