Great questions!

One thing you need to know is that no guard is unbreakable, un-passable. Stacking is a great way to set up a pass, or as a pass itself. However, the wedge pass is still very effective, even when your opponent’s legs are squeezing you tight.

Chances are, though, it’s posture control that’s making the guard tough to pass, not a strong squeeze. Check to see if his legs are controlling on top of your waist – if this is the case, push them down (without opening yourself to an attack) as low on your hips as possible. With good balanced posture, you can begin guard breaking by slightly leaning over on leg (not upsetting your balance), driving and driving one knee into the tail bone. At this point if the opponents hips are not down, the wedging won’t work.

Now, if you are having trouble getting the ankles to unlock, here are a few tips.

Grind your elbow into the medial, upper part of the thigh, four inches below the groin. There are nerves and arteries that pass through there and moderate elbow pressure can loosen up the legs.

Relax and make your opponent work. Keep your elbows in and your hands close to your neck. “Weight” as heavy as you can, reserve energy, and cover his mouth and nose with a cupped hand (or a gi if he’s wearing on). Burning down his energy will loosen his guard.

Set up the guard pass as a move #2 in a series. In MMA, just punch the face. Mental resources will go into head defense and guard passing becomes easier.
Fake a stack-attack then smoothly transition into a wedge.

In fact, try mini-body slams to loosen the ankle lock and slide his legs down your body.

On the flip side, to truly prevent stacking you need good posture control. Whenever the opponent has a stable base – three un-challenged posting points – he can try to stack. However, you can deal with the stack by seeing it coming and releasing closed guard and pulling De La Riva Guard or X-guard and attempting an immediate sweep. Even if you don’t know much outside of closed guard, release your ankles and don’t get lifted off the ground or have your hips get stacked over your head – you’ve lost control in these positions.

“Opening the door” philosophy is M O N E Y. Even most jujitsu players attack in a linear, uncomplicated way. With high guard control, just move those hips laterally, create an angle and tip them over into your mount. Or omoplata.

One thing I’ve noticed from wrestlers who aren’t aware of JJ tactics is that they don’t hold back and put their full weight into everything they do. I have personally found that the “opening the door” method of moving their momentum to tip them over, or let them pass to take the back is very effective. Most smart wrestlers will only go about 80% to get their dominant position but not risk having that motion continued.