How to station some of my hunters in a tower?

I've got a lot of dwarves hunting wildlife, and figured that I could use the marskdwarf training they're getting and station some of them in a lookout tower, in case of ambush.

I tried to accomplish this by creating a squad consisting of all 9 hunters and setting their order to (through ms) to station a minimum of 3 soldiers at a point. However, almost the whole squad spends all of their time there. Is there any way to let the rest of the marksdwarves continue huntint wildlife?

My personal preference is to set the dwarfs stationed as marksdwarfs indefinitely. Then, when you want to kill some animals, simply give them the kill command on various animals via the squad menu. The advantage to using this is are:

• you can easily station all dwarves in the tower during a seige
• You can choose which animals to target, so no dwarf attempts to singlehandedly fight a giant zombie elephant
• The marksdwarves will tend to shoot from a longer range, gaining marksman experience faster, at the cost of not gaining ambushing and hammering experience. (YMMV)
• Looking at the kill list lets you know what animals are around, so you often get a warning about those zombie pandas before the Urist was interrupted by zombie panda messages show up.
• You can choose not to kill certain animals that you like having around, for breeding or whatnot

Downside is that it takes more micromanagement.