hmmmm, not to sure try experimenting with the "Stop" command cuz for my when a unit is not moving they are using the "Stop" action... WE is not available to me now... but you could try this:
Event-
Unit issued to Stop
Condition-
Unit Has *YOUR BUFF*
*(im not to clear on how you abil. works so you might ned to change condtion)
Actions-
Order triggering unit to Attack *WHERE EVER YOU WANT*