Pretty amazing, how you learn even things you thought you knew.
My armbar from guard has always been terrible: I've spent years faking that move just to get to something else. I could never seem to get my hips shifted quickly enough: putting my foot on their hip was too big of a giveaway.
But yesterday, everything changed. Watch this video by world-class black belt of black belts Pedro Sauer: ignore the foot on the hip. Focus on the other leg. With no foot on the hip, you can swing your other foot across the person's back in one smooth movement, shifting your hips and catching them by surprise. So slick.