Power supply cable destroyed... again. (magsafe end)

This is the second time in two years. After some months the plastic that protects the cable starts tearing apart near the magsafe connector, all I could do was using some duct tape, even thought i know the tape glue is not cables' best friend, i didn't know what else to do. Now i am forced to buy a new power supply because the damage is in a point that i can't repair (or don't know how to.)

Anyone who had the same problem? Last year when i had to change it they told me at the apple store that the cable probably was run over by chair's wheels, which was NOT. It was not that time, it is NOT this time. Could this be heat related? I keep it always plugged when i'm using it at home. I'd like to avoid buying a fourth one for the same reason