Lets try to keep is real here guys. The OP's scenario was 8 widely separated house on a several square kilometer piece of property and roughly 15 people to defend it all with.
Which means at best 2 per house and in an attack (surprise or other wise) not a lot of manning of bunkers and trenches going to be happening. There is no where near enough people to maintain any semblance of a security watch over the distances involved, to provide any advanced warning, nor even to keep a watch in each house.
Any neighbor responding towards the sound of gunfire will be leaving their own house unprotected and would most likely just get ambushed. So each house would need to stand on its own in most situations.
The best they could do would be to fortify each house, with the easiest method being to pile dirt up on the outside to the height of the windows. Though in a non-SHTF world this is also the fastest way to ruin a house as the moisture and termites have direct access. Slightly more expensive would be to disguise this as a planter that extends around the house with some type of barrier film keeping house protected.
A more involved/expensive method would be to install bullet proof panels on the inside of all exterior walls with panels that can be installed over the windows as well. Could save appreciable money by not running panels up to ceiling.
Last edited by Steve_In_29; 04-29-2013 at 10:19 PM..