As an Army officer, I learned that in order to be effective, and army must have three key abilities: To move, shoot, and communicate. Take away any one, and you are ineffective. But if you get all three right, and you can absolutely devastate an opponent--even one that has superior numbers. The same principles apply to defending a survival retreat in a TEOTWAWKI situation. In the context of a static retreat position, movement is not as crucial, but don't overlook the need to conduct commerce, and even the need to move between retreat buildings safely. And in an absolute worst case, consider the potential need to vacate your retreat in a hurry. Always have a "Plan B"!
As for the other two factors: If your correspondence has been any indicator, I'd say that most of you have the capability to shoot well in hand! ;-) But be sure to consider:
1.) Engagement at all ranges within line of sight.
2.) Engagement at night. See my previous posts on tritium sights, tritium-lit reticule scopes, and Starlight Night Vision gear. Also consider getting some military surplus trip flares. (Unfortunately these are scarce an expensive, but they have a very long shelf life.) There is also a nifty gizmo made for chemical light sticks that works much like a trip flare: It is a metal light stick holder that can be nailed to a tree or a fence post. It has a spring-loaded mechanism that flexes a five minute duration ultra-bright light stick.to activate it. Clever! Here is something something even more clever that was mentioned to me by a friend who was recently in the Special Forces: Use infrared chem lights, and the bad guys won't even know that they've illuminated themselves. ("I pity da fools!") (To explain: Infrared light sticks throw off a glow that can be seen only through starlight night vision goggles or a starlight rifle scope.) The chemlite trip flare gizmos are available from several mail orders dealers including Nitro-Pak, Spruce Mountain Surplus, and a gent on Craig's List (I haven't done business with the latter two.) Just keep in mind that because of their relatively short shelf life, your stock of chemical light sticks should be kept refrigerated and rotated once every two years!
3.) Taking game without making noise. Consider snares, traps, and archery. See the Buckshot's Camp website (http://www.buckshotscamp.com) to learn about trapping and snaring. Buckshot has some incredibly educational DVDs.)
Now on to communications:
1.) Plan for communications with your neighbors to coordinate security. Obviously the phone systems will be down (both land line and cellular) When The Schumer Hits The Fan (WTSHTF) and the utility power goes out. Most telephone company offices have large backup banks of "floating" batteries, but don't depend on the phones to work for more than a few days after the onset of a long term power failure.
By now, you should have at least three or four military surplus hard wire field telephones (such as the venerable TA-1 or TA-312) and plenty of commo wire. Those are available from a number of vendors including Ready Made Resources (one of our advertisers) and Fair Radio Sales. Both of these companies are very reputable. Remember that if you use FRS, GMRS, CB, 2-Meter, or any other radio-based communications system that you should consider it non-secure (vulnerable to interception). Also be advised that most of these bands have line-of-sight limitations.
The capability for really long range communications (such as HF transceivers) may be a huge morale booster in the event of TEOTWAWKI. Odds are that you will have relatives living at the other end of the continent, or perhaps even overseas. Being able to relay messages back and forth to them will be very reassuring. WTSHTF that sort of reassurance will be crucial to keeping everyone at your retreat sane.