We've got... devices that stabilize the area around them, once we place them. The trick is mostly getting them spread out enough to cover the whole area.

[She makes a small gesture with one hand, and an array of semiphysical blue-bordered cards manifests in the air at her fingers. It fades as she makes a grasping motion though one of the cards, and one of the stabilizers falls into her hand - a couple of feet long, and shaped more or less like one of those bacteriophage viruses, with the cluster of feet on one end and the diamond-shaped core at the other.]

I don't really understand how they work - magitech isn't my field at all - but they cancel out the worst of the uncontrolled magic and keep things from coming through the fissure.