Rick had kicked Carol to the curb in the previous episode and had come back by himself. He and Carl had to fend off a "herd" of zombies that decided to push harder on the fence. Most of the others are sick, tending to the sick, or looking for medicine.
We discuss such things at work and this past discussion has once again brought up some recycled topics for us:
Idea 1 - get bigger gunsWe know from previous seasons, there are Hummers around. Certainly there are some with .50 cal mounted guns. Get some and park them for when the fence breaks ( see ideas 2 & 3 )
Idea 2 - tie a bunch of zombies to the fenceMichonne proved that you can just remove their jaws and arms, rendering them "not dangerous". Then tie them up around the fence. The prison will now smell like zombies and the other zombies will likely move along, thereby freeing you to garden and raise livestock.
Idea 3 - dig a big trenchFind a backhoe and drive it back to the prison. Distract the zombies and dig a big trench. Zombies will fall in, allowing you to burn them at your leisure.
Idea 4 - head to waterLeave the prison and head towards the ocean. It might take a while to get there, but most likely zombies can't swim, and there will be plenty of fish to catch for food. You can live on a houseboat. Reproduce. Rinse. Repeat.
It seems likely that they will have to leave the prison, rendering some of these ideas, moot for the prison, but probably useful somewhere else.
Oh, to be a writer...