I would also deem the first floor of the blue building, if caded properly, unbreakable. When you first produced that cade, I immediately thought "simple and fast to build = a noob's dream of cading" which then = new cade spot. But the fact is that it is unbreakable and thus that spot should be avoided. I just cade in one of the rooms with the two vending machines and that is sufficient. It allows zombies a good chance of tagging me if they knew how with a little teamwork.
I can tell you that "most" spots that James cades up can be taken down with a couple of deformed and classics. *Glimmer of hope for you noobs *
Or just bring in weeman and his force push powers....