I find one is enough, and I would find the sock thing counterproductive …the great thing about the lacrosse ball is, being rubber, it’s very high friction and won’t slide around on you when you’re up against a wall. Wide open areas like back, quads are more efficiently dealt with with a HARD knobby roller like the PhysioPhit. Hard to reach/awkward/deep areas (delts, piriformis, spinal erectors, etc) require the ball.