Tile that looks like natural stone should fit the bill. Just make sure it has enough texture to avoid those little feet slipping.

Try using clear epoxy on the surface. Fiberglass resin also would work to fill in the holes. Simply mix and pour into place and wait for it to harden. Google the products to purchase larger quantities as what you would purchase in the box stores would be to expensive and not enough.

http://www.wholesalemarine.com/p/HIB-701340/...