Magically fortified sandbag emplacements built outside the Reaver castle by Holger, Imani, and the strippers.
While Carl and the others plotted the interior of The Reaver Castle, Holger, Imani, and The Strippers built both a primary defensive position and a fallback position just outside the castle, using good, old-fashioned, magically fortified sandbags rather than anything exotic.
The positions absorbed the first shock of the Robot Doggies assault, with Holger calling out the incoming from behind them. They were rendered moot moments later when the castle detonated and the survivors were saved instead by distance and Imani's wing-spread shield.
Stacked walls of magically fortified sandbags forming a firing line and a secondary position behind it.
The party's prepared defensive line for the expected sentry dog counterattack.