It's not a big farm, so our tractor is a New Holland compact 30hp. We got it used in '08 and I have been very happy with it. However I think a stone hit the underside of a fender because a few years ago the paint started bubbling then the rust underneath collapsed leave a hole. So I cut out the rusty bit.
Then cut a patch to fill in
Then welded in the patch. I only burned through the fender near the edge.
And because I suck at welding, finished up with some fiberglass, primer and brushed on some New Holland blue.
From 50 yards you'd hardly notice. But hey, it's a farm tractor.