I use a sheet of Correx doubled up under a rug. The carpet beneath has pressure marks where the chair rollers have sat but the rug/Correx have taken the brunt. I tend to not move the chair, so the chair feet stay in the same position. The rug has indents where the feet sit but looks perfect otherwise.
For removing indents in carpet, I have used the damp bathroom towel and hot steam iron trick!
Grab a bathroom hand towel, wet the towel, ring it out so it's damp. Place damp towel on carpet, iron the towel and hit the steam button repeatedly - just do it in short bursts, e.g. 3-4 seconds, lift off, repeat, and keep checking carpet until the pressure marks are gone. Works well.
P.S. - Always try on a less conspicuous piece of carpet first.