Stacking that shit is a legit defense to the gogoplata. It puts alot of pressure on your knees, and if you have pain there then it means they aren't flexible enough to be in that position. I've never understood why people will put themselves in a position in a way that their body doesn't bend.
Stacking is a lame defense to the gogoplata. It is much easier to grab the guys foot (The one applyin the gogoplata) and turn it inward creating a toe hold. Then you get an escape along with a submission.