rustproofed

/R AH1 S T P R UW1 F T/
verb
  1. 1

    To make resistant to rust, such as by applying a coating.

    โ€œWe'll rustproof the metal with a good coat of paint and then we'll be able to leave it outdoors for years without damage.โ€

Source: https://en.wiktionary.org/wiki/rustproof, https://en.wiktionary.org/wiki/rustproofed