Air Strikes

[RonD]

Teleport/Cloud Trapeze a squad of 3, maybe even 4 or 5, mages, scripted 1x or 2x Rain of Stones, retreat, on top of his army.

Of course, you haven't told us what nations are involved, so you might not have Air/Earth mages. This also won't work if he has beefy air mages. If your RoS squad is on the fragile side you probably want to cast some form of mistform on your guys 1st, and hope he doesn't do the same. And you want to make sure you have a safe place to retreat.