Curious as to people's ideas as to what constitutes a good defense for both your initial redoubt and your final stronghold. Personally, I believe in the doctrine of "Defense in Depth" with ever increasing defensive attributes the further into your territory you go. One can define the areas of protection easily via color code, e.g. your outer layer and largest layer could be protected by something as simple as a triple concertina barrier and be known as a yellow zone.
My final redoubt would be a large tract of open land, farmland preferably, which will be surrounded by the aforementioned triple concertina. A small number of zombies will be halted long enough to be found by Romeo (roaming patrol callsign) teams and dispatched before they are able to penetrate deeper. I speak from experience, having laid out miles of concertina during the course of my enlistment and know how hard it is to move through this barrier if properly staked and positioned. If the zombies did in fact manage to breach the wire, it would leave obvious signs of their passage and enable us to know that there is an intrusive element in our yellow zone. The secondary layer, will surround the primary water source (small lake or pond) and enclose the arable farm acreage closest to the main base. It would be a double line of chain link fence with another layer of triple concertina in between. At several places along the defensive line, I will place "zombie traps", areas designed to be easier to penetrate and funnel any intruders toward a chokepoint with a pit or other entrapment device to hold them in place. Finally, the last line of defense will be build using the large metal transport crates they use on ocean bulk transports and railroads. A double layer (one stacked atop another) of these crates (standard ones can be 20' by 8' by 8') create a daunting defense for both zombies and human raiders. The main gate will be a bus or other large vehicle plated on one side (the exterior). For small groups (returning patrols and the like) a crane elevator system will be used for entry. For larger convoys of supplies or refugees, the bus will be driven to open the gate. Inside the gate area will be further enclosed with a strong wrought iron gate allowing entry to the inner sanctum.
As an additional measure, each building inside this last zone will be surrounded by hesco barriers (boxes made of canvas or ther fiber held into a shape by wire mesh and filled with sand/dirt/debris (used in forward deployed locations by the US military in addition to sandbags for defense) with a small entry way to allow access to the building itself.