Tired of losing your balance and getting pushed around by bigger guys when you're trying to block punches? There is an easy way for you to fortify your guard and allow yourself to block a solid punch without being moved:
…Just bend your knees and drop your weight a little right when you catch that punch on your guard.
It's very simple. Imagine your opponent throwing a punch at you. Right as it lands on your arms, you bend your knees, drop your hips and exhale at the same time. Lowering your weight allows you to temporarily anchor yourself into the ground and fortify your body structure allowing you to withstand a harder punch without being pushed around as you block.
You can practice this technique on the heavy bag. Stand right in front of it with your chest almost touching the bag. Push it hard to make it swing away from you. As it comes back at you, quickly throw up your guard, drop your weight and exhale. If you drop your weight correctly, the bag will crash into your guard but it won't push you back. (Don't focus on pushing back at the bag, instead focus on dropping your weight and pulling your body down into the ground to absorb the impact.)