There are air deflectors underneath the car, I think it's two at the front and two at the rear.
They are sacrificial bits of plastic.
I've now had 7 replaced in 10k miles.
Each time a bill of about £250.
I used to cringe when it first hit them but now not so much!
The fronts are rubbery and cheap, but I think the ones immediately ahead of the rear wheels are metal and more difficult to replace? I'm on my third set of front deflectors, I think they're designed to break away easily
There's rubbery ones at the front of the wheels/bottom of the bumper, then nearer to the wheels another set, which are the ones that your hear going over the speed bumps and bottoming out.
The rubber ones I've been quoted £71 for- never had one of those fitted as yet..
The others are a blade of hard plastic, which is slightly flexible.