[Mark_Nguyen]

Well, "In the comics":

...They did all that. In fact, the farm already had a defensible barrier and so on . They didn't spend nearly as much time at the farm before moving on, leaving Glenn there with Maggie. After discovering the prison and clearing it out, they go back to farm and convince everyone to move in with them. Since the winter had past and the undead meat popsicles were thawing out and attacking / wandering by more often, the farm gang was happy to migrate.

The prison itself eventually has its own farmland and already comes with several rings of fencing to protect against walkers, plus prison riot gear, a generator, tools and other weapons. It's a pretty tight place, but as it often happens in these sorts of things it's undone not by the hordes of zombies but by the humans within and without.

There wasn't anything bad with the TV farm, and the lack of walkers was acceptable enough. It wasn't proof against a horde though, and should another one come through a makeshift wall may not have been enough. A prison will have better walls for that sort of thing, and some of the later comics settlements they run into will have even better fortifications.

Mark