Then using a nulled sequence won't work anyway. It'll only drop one Sacred Shield and lock up until you change your focus.
Personally, I'd suggest using the priority setup and putting Sacred Shield down at the very bottom of your list. My Ret uses Selfless Healer ATM, but it's the same idea.
/castsequence [@party1target][@target] reset=5 Inquisition, Templar's Verdict, Templar's Verdict, Templar's Verdict
/cast Templar's Verdict
/cast Hammer of Wrath
/cast Crusader Strike
Of course, you'd change Flash of Light to Sacred Shield and @party1 to @focus. The extra Judgment in the sequence forces at least a small delay so it's not spamming FoL, you can add another Judgment it it's still spamming too much or some other spell that's not in the priority, like Rebuke to force a temporary cooldown, but it will give your other spells a chance to come off cooldown and cast instead of Sacred Shield.
/castsequence [@party1] Flash of Light, Judgment