I never really had any luck on getting autocasting abillities to work with Triggers, However you can use a simple buff check with an "On/off" abillity placeholder.
Basically, you need to create three abillities, A placeholder for the "On", One for the "Off" And an orb effect (Could be based off the Lightning attack lightning lizards have.)
Now then, Give the unit the placeholder abillity (Basically a dummy abillity, does nothing if clicked) And trigger it, So that when that certain abillity is used, it is removed, and then replaced by the Placeholder "On" Abillity, Meanwhile also adding the orb effect to the unit via a trigger.
Simple, when the "On" abillity is cast, replace it with the "Off" abillity and remove the Orb effect.