Do harder floors prevent tunneling?

Floor textures do not prevent your inmates from tunneling, but walls do. Brick walls take longer to tunnel through than open spaces. Fences have almost no slowdown effect. But by far the best way to slow down inmate tunnels is the perimeter wall which take really long to dig through. Unfortunately this wall is very expensive, so surrounding your whole prison with it might be outside of your financial possibilities. By the way: Large pipes speed up tunneling, so you should avoid placing them near the outer wall.

However, a much cheaper way to prevent inmates from tunneling is to prevent them from getting the tools in the first place. Tools used for digging are spoons from the canteen and workshop tools. Placing metal detectors at the exits of these rooms will catch most of them. However, metal detectors are not 100% reliable and there are also other sources of contraband which are hard to control. That means you should routinely search all cell blocks for hidden tools. The best time to initiate a cell block search is during meal- or yard-time when no inmates are in the block. This prevents that the inmates will be searched personally, which causes unrest (they do not care when their cells are searched, even when they are present).

As of version 1.0, tunnels still start in toilets and the only way to find them is the following:

• Metal detectors
  at workshop, visitation, canteen, kitchen and laundry.
  Workshop for the tools, canteen and kitchen for spoons and tools smuggled in food boxes, laundry for tools smuggled in laundry baskets.

• Dog patrols
  around the cellblocks. Dogs will irregularly flag potential tunnels. If they find tunnels in the same area over and over again, it's time to start cell searches in this area.
  If you choose the Warden who knows how to tunnel, dogs will not only flag but also find more tunnels outside the cells/cellblock/outer wall.

• Manual searches
  Regular cell, cellblock and prisoner searches will uncover every tunnel while it's still in construction. I do a cell search every second or third night (depending on how many flags my dog patrols bring up) and a good old shakedown every 10 days just to keep it interesting :)

Generally, I've made good experiences with a second fence around the whole map. In several cases, a prisoner already tunneled outside the perimeter/primary fence when his tunnel was found and tried to flee only to be stopped by the large fence.

To add to peper757's answer, tunnels always seem to start from toilets. Ive never seen prisoners start digging just anywhere.

You my see dogs scratching at the floor in random places but if they find a tunnel it will probably have started from a toilet.

The solution is to prevent prisoners from getting tools in the first place. Metal detectors at the entrance/exit of the canteen and workshop should help to reduce the burrowing.