There are lots of silent weapons, easily made and some that can take care of a number of bad folks. There are lots of sources that I personally have used and produced weapons from. I recommend the book The Poor Man's James Bond.
When one-on-one the following is listed in order of preference:
Up to three attackers could be taken on with a licensed shot gun; but more than that, assuming they are armed, will probably take you out. Best bet is to run. Or, if you are very skilled take them out using 1 or 2 above on separated individuals to increase your chances.
My biggest fear for any settlement is to be discovered by roving groups of deserted military, with their firepower. In such circumstance there really is no defense, especially should they have armed vehicles. Every community should consider their potential location such that natural obstacles would prevent military vehicles from getting too close should you be discovered. Escape plans should also be in place should your settlement become in danger of being overcome by foot soldiers who would possess much greater fire-power than can reasonably be maintained by an individual community. In such a situation it would be much better to abandon the site to live and build again another day.
Just my 2 cents.
Offered by Ron.