Sometimes we ourselves are porcupines, there's definitely one in all of us. When dealing with people like them, we first put ourselves in their shoes, what made them defend themselves. Sometimes the words we choose and the gesture we show can be misunderstood and people will start to defend, it's nobody's fault, the best way to approach is to interact calmly with that person and find out what made them defensive.
This book offers simple steps to love "porcupines". It addresses "porcupines" that are your lovers, parents, children and work place. It's an interesting book to me because I only know that when people are defensive I either become defensive myself or I try to communicate calmly. This book managed to offer more advice because it's written by a psychiatrist. Best to listen to experts who have studied on this subject and apply them. The more you practise the more it will become a norm to you :).