Boris Goodenough said:
The best defence I have ever seen is this:
beat that!
for me it would be:
barricade yourself in a caste. preferably one with a big patio inside so i can use some seeds for food and gather a bunch of people who arent morons.(thats hard to do).
why a caste? because it was build for defense and i can stab those fuckers trought the portcullis with the weapons in the museum on display.
plus if i am lucky i have a second wall with a nice killing field between them.
electricity will be a problem though.