For me, strong posture would be the first choice if not just post you leg up and then go back quickly to avoid any sneakiness
Whenever someone opens their guard for any reason my hands go to their hips and I push myself backwards into a combat base. A) You become to big for them to ever re close guard. B) Kill the hips you kill the sweep.
When opens his guard and starts to sit up for the sweep, push his leg down with your hand and step over it. You can force him into half guard or even take his back.
Good advice, ill have to try it. Thanks