This post from Taekwondo's Dan-gun session done April 17 2007 talks about two upper blocks against a downward strike. Following that are two knifehand strikes - one to the side of the neck and the other to the nose. A good variation of techniques from Dan-gun to practice with a partner.
The first ran some defences from an overhead strike. The drill centred around two upper blocks (Chukyo Marki), the second being an elbow break or strike to the triceps. We modified the timing slightly so that the upper blocks are done close together - meaning the second strike is done very quickly after the first. Then leading hand is pulled back into a vertical shuto (Soodo) striking the neck or back of the next. The second shuto breaks the opponent's nose. This session we looked for accuracy in the upper block strike and a modicum of control over the opponent's arm and body.
I'll add that after the second upper block - aimed at disabling the attackers limb, the first upper block turns into an arm control. The hand is wrapped all the way around the attacker's forearm or wrist and pulled backwards to the ribs - like a hikite or reaction hand. The knife hand strikes the side of the head - and then in turn changes into a control, either wrapping around the neck or shoulder so that the second knife hand strike can sink into the opponent.
Dan-gun Defensive Drills Against Strikes