Whilst I believe Tyson's defense is (like himself) the stuff of legend (and I mean that sarcastically) he did not get rocked very often, I mainly explain that by looking at his opponents and understanding that the overwhelming majority of them feared retaliation rather than wished to inflict damage.

I believe Tyson was phenomenal but he has become like a folk tale hero and people freely exaggerate about how great he was and honestly he had a very weak era until later in his career and he was fed loads of tomato cans early on.