Singlespeed & Fixed Gear - Chip resistant paint?

So, I painted my bike, and I'm very happy with it...I used car enamle spray paint, primer, of course, and clear coat, but it still chips relativly easily. Does anyone have any advice on how to make the paint as hard as a rock? Some chipping is expected, but not at this level..

polyurethane is generally very hard, can sometimes be slow to dry depending on the type you get.

enamel is usually pretty decent, did you use enamel with a hardener or just straight enamel?

i'd get a hardener with it next time if you didnt this time.
where did you get the paint? if it was in spray cans from like pep boys it may not be the best paint.

I'm thinking of stripping the flat black paint off my Bianchi Pista which is riddled with chips & gashes. I was thinking of using a cheap can of rustoleum spray paint and coating it with some polyurathane clear coat. Would that suffice?