In stead of worrying about your own guard, you should let your opponent to worry about his guard. You need to move your fists closer to your opponent's head than to allow your opponent's fists to be close to your head. In other words, if you don't give your opponent enough space to generate his fast and powerful punch, you will be safe.
How to achieve that? You will need to "occupy" the space between you and your opponent. Try to fight in your opponent's territory than to fight in your own territory.
How to achieve that? You will need to "occupy" the space between you and your opponent. Try to fight in your opponent's territory than to fight in your own territory.