Maybe not prevented entirely, but discouraged. For example:
- A reduction in points/score/money if you spend too much time and/or kill enough opponents in the same area.
- A bonus for killing a player who spends their time on the same spot. The higher their killcount the higher the bonus.
This way it could be considered a valid strategy, but the game would still aknowledge that it's a cheap one. If the camper's rewards for a kill lowered by, for example, 5% for each consecutive kill, but also rises the reward for killing them by 5%, it would encourage players to move around the map.
I'm a PvP newbie, but I feel this could work.