If these are leather you can use several things:
These are made of hard plastic:
http://www.amazon.com/Traveler-Plates-Nails-Black-Plastic/dp/B0031ELG50
These are nylon:
http://www.ebay.com/itm/10-pr-Guard-Heel-Plates-Toe-Taps-Nylon-Plastic-Shoe-Repair-10-Pair-with-nails-3-/252267586149
These are metal:
http://www.ebay.com/itm/DIY-metal-BIKER-work-BOOT-CLEATS-PROTECTOR-heel-toe-GUARD-W-nails-REPAIR-shoe-/111945202694
These are hob nails, worked well for the German army:
http://www.najecki.com/repro/shoes/Hobnails-R.html