Detecting "Starfall"

I have been making custom spells for a while now, and I now want to make a new one. This one will require a trigger to do what I want (another thing I have done with several spells before) but this time its a bit different. Instead of detecting a storm bolt cast, I need a channeling spell. (i.e. Starfall, Tranquility, Death and Decay, etc) The spell effect needs to happen the entire duration of the spell, so is there any way to detect whether a starfall-ish spell is in use? I could detect the cast, but then I wouldn't be able to turn it off when it ends, since there are many ways to end it. Any one have ideas on how I could have a trigger check whether the unit is using his channeling spell?

I think this belongs in another forum.

Oh crap, I had this open in two windows and musta used wrong thread, could some mod move this?

A genearl idea.

First add an if clause in your spell (a loop more then likely), if the caster is in unit group then continue with spell. Add a second trigger within this function, give the required events (most likely the three order events), check to ensure which unit is ordered is the correct one, then if the condtions are meet calls a function that removes the unit from the unit-group, the conditions will be set to false so the spell stops.