Every weekend after all your drives are over bring your car to your trusted carwash and have a full wash. The place I go charge AED 45 for full wash + vacuum - they wash the under carriage and engine bay. I don't go to the fuel station anymore - but at the fuel station too if you ask, they will wash the under carriage. But sometimes they end up charging for a special steam wash - either way they cost more.
I avoid cleaning the car at home or at malls etc., as they tend to leave swirl marks on the paint (not that all the sand bashing helps - but still) and it is economical for me to go weekly wash. For 200 bucks a month I have a car that I can pass it of as lady driven on any weekday.
PS: once I was sold an undercarriage waterproof treatment - anyone else got it? Got it because of my inability to say no. But I am glad I did it because the undercarriage does get drenched every week.