Unit is given Order (cast-spell)

The most common way to make a trigger-based spell seems to be by using "empty" spells that drain mana and have no effect, and making a trigger that detects that and creates the spell effect.

I've been trying to get this to work, and although the listening to order works just fine, it does not pay attention to whether you're in range or not - you can cast Fireball from all the way across the map... that's just not right.

I tried putting a condition that the unit has to be within range of the target before casting, but then the unit walks up to in-range and casts the empty-spell Firebolt, using mana but doing absolutely nothing.

Is there any way to detect the actual casting of a spell, instead of just listening for Orders given?