For a couple of decades I've made and used pocket protectors for my keys. I have house, car and all sorts of other keys in a big bunch, including a couple of small padlock keys. These keys go through pocket material faster than a kid through candy floss if there is no protective pocket.

I keep my keys attached by a string to a souvenir-of-Corfu leather pouch which is finally falling apart after 25 years. It's to protect me, not my pocket. I have a nickel allergy and enough nickel gets through cotton to produce a raw bleeding patch on my thigh.