There are very specific spawn areas that can only be corked by building a Workbench within the spawn point's radius.

Take regard to the workbench radius, and build a workbench along your spiked fence so collectively you could build anywhere within the fenced area. Nothing should spawn in that area.

The problem is, the latest patch makes enemies 10x more aggressive and will attack your fence more than you! I've watched enemies run away from me and attack my walls during an ambush. Talk about ridiculously stupid AI :P