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 bought a length of plastic leather material from a flea market some years ago and also a large reel of what might be called knicker elastic. A pocket of the material is attached to a key ring with the elastic. Even if a small hole appears in a pocket the keys wont fall through.

A protector lasts between six months and a year. This reminds me I'm just about due to make a new one.