I would leave the back one down so you keep stuff of the wall. I would keep a vacuum cleaner handy for anything the lands just outside the cage. BUT night time is time for them to run around, play around, LOOK around. I would NOT put up a wall so they have nothing to see. Ours will see us and jump to the front, looking for a treat, or a ride on our shoulder, or a jump in our shirt. They check out the dogs and kids. To put them in the total darkness? during their awake time seems very wrong to me. they have good nighttime eye sight, but with a full cage cover will they even be able to see in almost total darkness?