Invincible Base Shields

I coulda sworn that someone on this site told me how to use trait zones to create invincible base shields. Did I just dream this? Because I can't seem to get it right. If I remember, this was supposed to work as long as the trait zone was touching the base shield. I've tried setting damage resistance on the trait zone to 'invulnerable' and I've tried setting the damage/melee modifier to 0%. Neither has worked. I've tried going back through my content for the answer and googling the problem to no avail. Does anyone know how to do this? Or did I just make the whole thing up?