Trap the Convoy

Throw land mines onto a mountain road. Stop the army convoy before it reaches your fortress. If one truck gets through, you lose. The drivers watch the road. If they see your mine in time, they drive around it. So throw it late, when they have no time to turn. Or drop two mines side by side and block the whole road. Fuel tankers blow up and take other trucks with them. Engineers dig up your mines. Raiders race past the traffic. Tanks need five mines to stop.