Yea alliances can't be prevented, since they're already occurring. The point is to try to get guilds to go to other towers to increase activity everywhere else as well. That's why they can't re take the same tower. Like you see whenever chain of memories has a tower its most likely deadwood they're free to return to deadwood but they have to take another tower before they can do this though, keeping them mobile. This will prevent them from taking deadwood again they have to give a new tower a shot for a change. Same for other guilds like risque who favor sardon. The extra points are an incentive to try and visit every tower. Guilds can try and trade towers but thats the point of having a certain time you must hold the tower for. You can't just trade you still have to defend it. And with many guilds trying to gather their points quickly it won't be so easy.