The reason why it is always there is because dirt gets trapped in the inner fender under the rubber fender liner, I learned this the hard way on my 3 gen. The easiest way is to prevent rust is to remove the rubber fender liner and when you wash your car always clean inside the inner fender so far my Integra that I purchased new in 97 still looks perfect and my 6 gen even though its not that old is looking good also.