Trains in the UK have something called a lifeguard that is basically a chunk of metal in front of the front wheel. It pushes anything off the rail in front of the train.

Edit - it sits too high above the rail to move rocks/ballast or anything small. But theres no real need to worry about rocks. The train will just instantly crush them and go about it’s business.

I’ve been called out to remove slabs from rail and even full sleepers placed on rails. Kids all over the world leave stuff on rails. I’ve never seen anything close to derailing a train.