Cane corso puppy potty?

ive got a massive 8 metre by 3 metre run for my puppy for while im at work ( no i dont have no one to look after him during the day) and was thinking that the floor is made of concrete he hapily sleeps in his cosy kennel but i wanted to put something in one corner for him to do his poo and stuff as its hard to clean it off the concrete so i was hoping someone had a suggestion as to what i could put there e.g sand, plastic lino...