Many "combative" self-defense arts don't advocate hard blocking. Most of the protective element comes from having a strong stance. For example, I prefer a kickboxer stance. It's difficult to hit any of my vitals even when I don't actively "block." Obviously, sometimes I do have to block, but normally I prefer a deflection rather than a hard block. I try to keep my blocks tight (can't think of a better word), like a boxer. Or, I may use some very basic trapping and move into a lock or throw. Anyway, I don't really plan my blocking, since in a real fight, I'll move instinctively and fight on from there. Whatever keeps you from being hit!