Door only way to stop decay?

I have these pillar foundations around my base so people cant build stairs up to my upper floors. I heard placing camp fires and turning them on and off will stop decay but I’ve been doing that and the pillars have decayed down do I have to let it burn a log or something or are doors the only way to stop decay?

It would probably be a good call to try letting the campfires burn a couple logs before turning them off again. I’m guessing that when a log burns and makes charcoal it updates the campfire which would update the foundation as well. That’s just a guess though.

only opening /closing a door and adding an attaching foundation tot he existing one.