Unnatural so maybe not welcome, sorry if so, and wont work if you like to live a chemical free lifestyle, but the best cure I have ever had for cracked heels, and I mean it works, is ~
Krazy Glue
No, I'm not nuts - you fill it up, it may sting a bit at first - but it stops and the gap closes, you can sand the crack a bit with an emery board or pumice after it dries, and it stays that way for good, it heals naturally, or is that unnaturally, and doesnt hurt again.
I had cracked heels up to an inch long, and some very deep...not a problem any more at all, first sign of one and out comes the Krazy Glue. I'll deal with the consequences later, cause I can walk for now! The generic stuff works too, I get it at the dollar store.
Tina/tfpets