User blog:Commander Starter/Spawn Problem

A few days ago I rebuilt and moded a naturally spawned village for a fun challenge. After the fact I noticed the villagers dying off. I staked out and noticed they were being killed by zombies. I don't understand how this is possible, since the entire village is enclosed by a 4 1/2-Block high wall, and is lit by Redstone street lamps. So how are the mobs getting in/spawning?UPDATE: Thanks to Dak's comment and my skills, I have solved the problem! Although, there are still some Creepers wandering in the corn fields. (Creepers of the Corn... Haha). So I still need help! If you can solve this problem, please try to relay it to me. You know where to find me.