I have a Jan 2002 M800 It ecels in mileage till date with

I have a Jan 2002 M800.It ecels in mileage till date with around 14 km/lit in city and aroun 20kmpl on highways in a consistant manner. Every thing has remained sound exept for the fact that the under carriage of both front fenders just behind the front wheels regualarly get corroded and I patch repair them every two years. Do I have a permanent solution to this problem? Its true the car faces waterlogged roads of industrial areas of Kolkata.Do other cars face similar conditions under similar situations. Please note i love this baby and cannot sell it.