You can buy caster protectors which are little round plastic cup things that you put under the wheels. However, these will probably leave an indentation too. Have a search for them and see what you think.
I work from home and just moved into a new house with beautiful cream carpet in the study. I have an office chair which is on wheels and worried its going to ruin the carpet. I know you can get those plastic sheet things to put underneath them but I really hate how they look.
The only alternative I can think of is a cheap rug or carpet offcut. But would this protect the carpet? Any other solutions?