There is another option; If you don't want to fit flaps just use 'clear skins' or 3M car paint protection film (made from clear vinyl) 'almost invisible'
Look at where the heaviest road grime sticks to your car then you know the shape you need.
Best to cut them so they fit the wheel arch face, underside of the sill and just up the side of the sill as this is where stones will damage your paint.
It is very hard to spot them on your paintwork once fitted, so it does not detract from the car's look and when if it gets damaged you can simply remove the film and replace with a new piece.
You can buy it on Ebay or from most auto parts shops.