Harder feet...try walking a round with no shoes on...get those trainers off and go for a walk around the block.softer shoes or harder feet
Alternatively, you could go to the Chemist and buy some "Alum" I am pretty sure that is used to toughen skin.
Soaking feet in very salty water will help, and as said, running bare foot on Dirt as well...so at a golf course or something...
Or, a quick Google...http://www.tuffoot.com/about/humans.htm
Says amputees use it as well, when wearing prosthetics, so you could investigate that avenue.