Complex sentence: The other prisoners have all become walkers, who are just aimlessly walking around in a walker-encrusted fenced off area and some people reanimated as walkers after being gored through poles.
Split into simpler sentences: The other prisoners have all become walkers, who are just aimlessly walking around in a fenced off area. Inside the walker-encrusted fence area, there are also some people reanimated as walkers after being gored through poles.