I keep breaking my iPhone 5 chargers?

I've had about 5 Apple iPhone chargers since I got the 5S a few months ago. I keep it completely flat on a surface, and it always finds a way to break itself. I'm fed up with it. The one I have now has just broke. It seems to have a little slit at the very top of the cable, beside the little plug (I don't know what you call it) that you put into the phone. Urgh!
How do I keep them from breaking? I heard you can put the spring from a pen around the top, how do I do that?!

Chargers, or cables? If it is the cables, treat them with more care. Avoid tugging or stretching them, especially at the joints.

A research shows that roughly 60% of all apple device chargers are broken.