5.) Every serious survivalist should watch "The Outlaw Josey Wales" for tips on how a small force can outlast a larger one from a well-defended fixed position in a fire-fight.  If you haven't seen it, do; but, in the meantime, just know that what I'm referring to specifically is where the characters fend-off an attack from within a Texas ranch house that was previously fortified to withstand Indian raids.
I think that covers just about everything from the standpoint of proper fortifications.  Undoubtedly, I'll think of something else I wanted to add after I post this, but it's already a long article, so it'll have to suffice.  As always, thoughts/critiques/concerns, etc. are welcomed in the Comments section below.
Some reading (pertinent to this subject) that you might enjoy:

"Patriots: Surviving the Coming Collapse" by James Wesley Rawles
"Survivors: A Novel of the Coming Collapse" by James Wesley Rawles
"The Medieval Fortress: Castles, Forts, And Walled Cities Of The Middle Ages" by J.E. Kaufmann & H.W. Kaufmann
"Survival Retreats: A Practical Guide to Creating a Sustainable, Defendable Refuge" by David Black
"Life in a Medieval Castle" by Joseph Gies
"The Survival Retreat: A Total Plan For Retreat Defense" by Ragnar Benson.

### Language ###
English

### Assessment ###
The task could be about recommended survival-themed literature, specifically focusing on books about defensive retreats.

### Query ###
Tell me good books dealing with survival retreats and fortress construction.
Tell me good books dealing with survival retreats and fortress construction.