Working out if a Layer exists, and if it doesn't, then create it.

Hello, I've got a problem and I can't seem to find a solution.

I have a simple script that creates a gameObject from the editor. My problem is that my enemy should be on a Layer named "Moveable Enemy", I can do this using c# to place it on the desired Layer. However, I'm planning on giving my script to a friend who might not have the "Moveable Enemy" layer setup on his machine, so I need away to search for a layer, and if it doesn't exist make it.

Any idea's how to do this?