Good chip resistant paint

Hi I am a taxi driver in glasgow and I would like any suggestions for a good chip resistant paint for the metal frame of the wheelchair built in ramps in the rear of the cab I have tried a few but they all seem to chip easely due to them being scuffed by the passengers feet, I don't mind paying a bit extra for a good product I have tried Hammerite and some others. Thanks for any help from Edie..
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