What they need is a prison on a river to spread out from. A nuke plant would do equally well since they are naturally secure and located near bodies of water usually. Water wheels are ancient. Herschel or Carol could figure that out. Feudal is a good point though.
A nuclear plant would be great, if it was still functional. They’d have power for year. A hydro-electric dam would actually be good as well, they usually have large interior space, and only two approaches that are easy to see. But there are not that many of them.
I felt like their prison was pretty close to water though.
One other point about this show — when Carl was pointing his gun at the boy, and they had told the boy to DROP HIS WEAPON, and the boy wouldn’t drop the weapon, and instead just kept walking toward him, I was yelling “Shoot him”. Because I knew that kid could swing his gun up and shoot them both at any moment.
If someone points a gun at you and says “drop your weapon”, you drop it, or you die.