Paint bubble on wheel

[Ash1751]

Hello,
Today whilst checking pressures I noticed one of these on two of my wheels.

I think think it was from pre refurb (as there were a couple of areas that weren't quite smooth that I noticed) and has got like this over time.
Two questions:
1) Any ways I could have stopped this from happening?
2) Anything I should put on it to prevent it getting worse?

Pretty sure that it can't be undone without a refurb, but if it can let me know!

Thanks

 

[Chrisgti6]

Looks like a stone chip or something to me, and it's allowed water under the lacquer.