Properly cared for, tools should last you a lifetime.
Shovels are one prime example of this. While they do take a considerable beating in the garden, you can still get years of life from them with a little simple care. One easy way to care for the shovel blade is to fill a large plastic container with sand and oil. When you done using the shovel for the day, dig the blade into the sand/oil mixture and move it around a little. This will not only clean the blade, but the oil will also keep it from rusting. Just make sure you store it where any excess oil dripping off from it will do no damage.