Spell shield and triggered spell effects

If I have a unit targeted spell that uses a trigger to do its effect, how can I stop the effect done by triggers when the target unit has spell shield which will block the dummy spell effects while keeping some art effects and triggering the "unit starts the effect of an ability" event. So basically what I'm saying is that there is no way to block custom triggered spells with spell shield. Or is there any?

you could always cast a dummy ability at the begining of the custom spell to see if it gets blocked or not.

By making it add a buff for 1 second ?

Well, I couldn't really understand the finer points of your post very well. Did you try 'Event: A unit starts the effects of an ability'? If that doesn't work, why not just add this to the spell trigger: 'Condition: (Target unit of spell being cast) has buff (Spell Shield)'?

Eh I don't know if it is as easy as you make it sound, I will test it now though.