What Wolfe meant by a secondary defensive system was the Lightning Sprite, along with a [Shock] inscription. Both would defend the doors indefinitely, stun anyone who tried to enter without the talisman, and keep the arrays safe.
Inside the building, it was mostly open space, with four guard towers watching the workers' movement inside. They did have a constantly running sink though, so maybe they weren't guards, but water quality monitors. Either way, they would notice right away if something went wrong inside the facility.
"This room here is a good one. It's solid and secure, but it's not used for anything at the moment. It was intended as a chemical treatment storage room, but we haven't maintained a supply at that level in decades, so this room just sits empty, while others store the chlorine in case of emergency." The Coven Leader explained.
