How does Santa claus cope with reindeer s#it flying at his face, at high speed, while riding on his sleigh?

Most probably during his younger years he had been trained as an astronaut.

He made an example out of the 10th reindeer--the appropriately named Dumpy. Dumpy was made into sausage. He reminds them about venison, the food chain and the hundreds of hungry elves that he needs to feed 3 times a day, 365 days a year. The other 9 reindeer now know better.

We're talking about enchanted reindeer here. These supernatural creatures do not produce waste matter so nothing would be flying at Santa Claus.

1. He likes getting pelted with it

2. He wears a protective mask (like a welders helmet)

3. he sewed their bungholes shut

4. he stops for bathroom breaks