At a training seminar, Rich P. and myself were training partners on Friday. We were working on knife deployment from grappling positions. This particular position was guy on top, you on bottom, and you try to deploy your knife. Your partner gives you a struggle and tries to prevent you from knife deployment.
Anyways, we found some success with the closed guard. From a mount if you can get your hips under him you can move to this position. From an open guard if he is trying to go for your knife or prevent you from going for your knife on your hip, a closed guard helps. You can besically can create distance between your hips and his hands, use your legs to help control his arms/hands, thus freeing your hands to deploy the knife. I'm fairly confident with this tactic because I was able to have some success with Rich giving me trouble; and Rich is 295 lbs. with a very long reach.
I will play with this more in our Combat Researchers Guild, though, and see where it goes.
Paul