Here where I live in Sweden we have winter-roads 3-4 months per year.

The roads are therefore sprayed with sand and/or salt part of the year. This causes the cars to be sprayed by other cars with sand and salt as you drive. When you drive through this fog of sand and salt some of it makes it on to the front of your car. On top of this the winter-tires that are mandatory also bring larger pebbles on to the major roads (the tread pattern is made in such a way that pebbles stick to the tire) and when the speed picks up the larger roads the stones releases, quite often upp in to the air, and moments later comes you and drive in to the pebble doing 100kph.
The pebble usually ends up landing on you windscreen, bonnet or headlight, where the windscreen cracks and on the hood you usually get a fairly big mark and the headlight cracks.
This has become a larger problem after cars was started to be equipped with plastic headlamps.
(EU regulation change to make decrease accidents and plastic is less hard than glass, it also lowers the fuel consumption due to lower weight. But you as user loose in durability)
The plastic in my headlamps are constantly blasted with sand during the winter and this makes the headlamps less transparent, On my old car I have replaced the the complete headlamp assembly on both sides due to the heavy frost effect that was seen after a number of years.
On my new car I have a more complex headlight assembly. It contains a Xeon/HID headlight with dynamic and static curve light. The assembly is expensive and worth protecting as a new one is expensive to buy and fit.
After some investigation I found that I could protect my headlights with plastic film. The film is actually originally made to protect helicopter blade tips.
The film can be purchased pre-cut to fit your car headlights and is actually possible to cover the whole car with this film. A another application for the same type of film is the screen protector film that you can purchase for your cell or mobile phone.
The film can easily be applied to the headlamp assembly glass and will give you a long lasting protection.
Protective film are made by several manufactures. This is just a example on YouTube on how easy it is to fit the film.
If you want you can cover the whole car with the film. That is maximum protection......