Thanks for looking. I was trying some alternate methods after reading up on physics and forces (didn't realize I was working on the shared file). But whether using physics or solids and bullets, the outcome is the same: as soon as the barrier objects are moved, the ball objects flow outside the barriers.
My hope was to eventually create a maze of sorts, so the thicker barriers are not ideal, but I'll give that a go. Given what I'm trying to do, what is the better approach: physics, or bullets and solids?