The box your dad made is nice...I like their room, too.
What about maybe putting a litter box in that spot, with just a piece of carpet in it. See if he might use that, then add just a little bit of sand on top of the carpet piece, then more sand, more sand...until the carpet is covered. I think I saw that 'trick' somewhere, can't recall.
What about maybe putting a litter box in that spot, with just a piece of carpet in it. See if he might use that, then add just a little bit of sand on top of the carpet piece, then more sand, more sand...until the carpet is covered. I think I saw that 'trick' somewhere, can't recall.