fender paint touch up

[sweaver76]

I trimmed my front fenders so my larger tires would fit better. I grinded down on the fender's edge and am wondering what I should do to best prevent rusting along that area.

I also banged the back bottom corner back a little bit and the paint flaked off. What can be done to rust proof it. It can't really be seen, I am not too concerned about appearances, just the rust.
Thanks.

 

[MONMIX]

Sand back all the flaked metal. Prime it and paint it.
That would be the method if you don't see it and you don't care what it looks like.