How do I protect my nice clean floors from snow and salt?

Could you set up a spot for them to remove their shoes/boots?

Minnesota ideas! All shoes/boots come off immediately at the door on a 5 x 7 rubber back textured water and dirt mat/rug. The mat/rug has a heavily textured area to catch dirt and grit. With a lot of snow on the mat/rug melting it may have to be hung in the basement to dry out in the evening because the rubber backing prevents the moisture from soaking into the floor and this kind of rug can get soggy. This doesn't happen often. Only when the grand kids visit and spend the day playing in the snow. All shoes/boots go immediately on a plastic boot tray in the closet or under the bench in the entry way to melt the snow and dry. This area may need to be vacuumed daily.

Make everyone take off their shoes on the rug right inside the door.

Hi ! Keep a boot tray next to the inside doormat and have everyone put their shoes/boots in it before walking through/ into the house !

We have a bench and rubber mats for the boots beside our door. A cute board or farm style sign "remove boots here" or something to that effect would help above the bench. I am not afraid to tell people to take off their shoes/boots to protect my floors! Anyone who lives in harsh winter climates knows it is common courtesy to remove boots indoors.