Skills and items are fire & forget, they don't last longer than on the action in which they're used. If you want a skill to have lasting effects, you'll need to work around this limitation. On a basic level, this usually involves the use of troop pages, common events, and states. Based on what you want to accomplish the solution can vary wildly, so we're going to need more detail before we can help you. What is this skill suppose to accomplish over the course of three turns?