For serious corrosion resistance I would suggest getting the slide coated with Cerakote. This stuff has better corrosion resistance than most other coatings and much better than the stock M&P coating. I listed a link to their product testing guide compared to other coatings. The only bummer with Cerakote is that its not as "hard" as other coatings and will wear through faster than most other harder coatings that are less corrosion resistant. For example, Cerakote vs a Kydex holster will be a losing battle within a few hundred draws. I am not sure about Cerakote vs leather, but I would assume that its not as abrasive as kydex. If you are interested Rick Hebert Firearms does Cerakote and can get whatever color you want. Check his website at www.rickhebert.com

https://www.cerakoteguncoatings.com/...de_1_10_18.pdf