Trigger Help

[THISisntDOTA]

I'm looking for the best way to tell when a channeled spell has been canceled using GUI. I'm using casting dummies which need to stop casting if the spell is interrupted before the full duration of the spell is over.

My spell is based off of siphon mana.

Some things I've tried without success:
* A buff comparison on my target (siphon mana doesn't buff the caster or his target)
* An "order comparison" for my hero

The first option could solve the problem if I was aware of how to add a buff to the target of siphon mana.

The second option could solve the problem if I knew the possible strings you can use for an order comparison. (the preset order in the comparison is stop)

Any other ways to solve this problem are welcome and thanks in advance.