I don't think anyone mentioned this, but there's a good movement you can use when you're underneath. Frame, but keep your arms in and you bridge and kinda shake/shimmy their hips down to yours. Once your hips are under theirs you again bridge and roll them towards their under hook side. They should flip over or you should at least be able to sit up enough to shrimp away. Also, just work on using structures period. It will really help your movement in bad positions. If you don't know what I'm talking about talk to Sean Applegate or Brandon McCaghren.