Ask HN: How do you protect your wood floor from your rolling chair

I telecommute from home, and my house has wood floors. Gorgeous soft pine, to be exact.

The problem is a standard desk chair will kill these floors.

I used to use an office-store standard sheet of thick plastic to protect my floor, but it's too small. I'm constantly rolling off of it.

Now I'm trying some foam rubber floor times I picked up at home depot, but the chair slowly flattens them, which makes the one that I sit on ever so slowly too big to fit.

Anyone use any kind of large floor protector? What works well?