Best way to prevent rust on bastard file knife

[Vpetrell]

So I had a knife made for me out of a bastard file. I am going to do te handle work and sheath for it

Anyways, what is the best way to prevent rust from forming on the blade after I get everything finished.

I did put a forced patina on the blade with a soak in some vinegar, but noticed some minor rust on the area he left textured with the rasp lines.

Is there any other finish I can put other than oiling my blade after each use? Anything permanent that will help?

Let me know.

VP