Forcing multiple units to cast the same ability

I have this area of effect ability that replaces the normal attack ability.

My problem is, that when I have multiple units selected and orders them to cast the ability, only one of them will do so. This has never been a problem before, but now it is.

I know that I could do it with triggers and add units to a group when selected, remove them when they're deselected and when the player casts the ability, order all units to do so, but I don't like that. I don't trust that method.

Does anybody know a simpler, faster solution?

when the unit is issued an order to cast that attack ability, pick all units selected by the player and order them to do the same thing, same target?

But that was what I didn't want.

Channel has a field, "unique cast" that supposedly handles this. It otherwise depends on the ability, stuff like roar is only cast by one unit, while bearform is cast by all units selected.

It's based on Volcano, I can't base it on channel.

well you can try to sit down and wait till wc3 listen to your prays and does exactly what you want automatically without you having to use methods you don't like

Then Vex's solution is your only option, its a very small trigger, nothing like the one you said in your first post. By the way, does volcano stack? If not there isn't any point

Ok, everything is perfect now, I misunderstood Vex first and didn't know that method. Thank you Vex :).