My opinion:
-Kevlar/Aramid belted tires stop large objects, nails etc.
-Urethane tire liners stop glass slivers, nail points, etc.
-Using both stops everything.

Tire liners need to be installed carefully: feather the edge with heat or sand paper and use plenty of talc to prevent the liner from vulcanizing to the tube. Get the right width for your tire and be mindful of installation and you're golden.

Oh, and thicker inner tubes do not protect against flats. They do, however, slow down leaks, both due to punctures and general air loss through the tube wall.