When setting up an outpost, carefully consider where you put them, outposts are the most efficient way of killing Zombie Hordes, but they will not protect you properly if they're placed poorly.
When setting up your first outposts at the church, consider putting outposts in places such as the construction site to the north or the house to the south of the road leading to the Church. This will prevent one or two hordes from reaching your Home.
When setting up additional outposts, try putting them at street corners and areas with a lot of buildings, this will prevent infestations from growing too close to your Home and can make walking out in the open much easier.
Moved to a new Home and want to move your outposts or simply want to put them somewhere else? Head to the Home page of your journal, select the outpost you want to destroy and press the green "X" button. It will take 1 minute to take down the outpost. The only downside is that if all your outposts are out of resources or two have the same resource, it's impossible to tell which is which before taking them down. Unfortunately this means trail and error.
Again, outposts prevent zombies from spawning within the Safe Zone circles, but they do not prevent the stragglers from wandering in.