After determining the size of the army, 200,000-300,000 strong. As you leave you encounter a patrol and decimate all but 2 of them. You steal all you can and run away before those 2 can report your presence.
They destroy the bridge at Skull Gorge and run on to Drellin’s Ferry to warn them of the size of the approaching army.
They setup the town militia as scouts and post riders to warn when the army begins it’s march. They also direct them to mine and trap the town before moving out.