Excellent ideas from many people.
May I offer a different strategy? Focus on training your people to be marksmen level shooters at least and plan to bug out if faced with overwhelming force.
You temporarily give up your position and come back at them at your convenience.
Static defense is too expensive.
Spread out your spider-holes and BOB all over the place and become a Grim Reaper at night. Hit hard and disappear. Over and over.
The psychological effect is devastating.
Use paintball to train.