What to use to fill in small holes in metal

my 2p worth<from uk> i had some grot on area on flat panel under windscreen it looked pretty bad, a scraped it back and all it turned out to be was a hole couple of millimeters....... with filler over it the bit literally burst the filler away cracking paint and looking real crap.....time to get nassty as you only want to do this once....get your grinder <goggles on> and cut that tin worm cancer till you see nice shiney shiney...:cheers:weld it however small and grind back, weld grind...<good practice time> de grease then acid etch primer, filler ,primer and if to be left outside or used until respray a coat or 2 of aerosol colour as a stopper as primer/filler not waterproof....