Litter Boxes

We have two cats and two litter boxes and I noticed the other day that both cats use one box as a urinal and the other as a ... non-urinal and how the heck did that happen? Is that a natural thing cats do? Was there a conversation about it? What about an accident? "Dude, what are you doing? That's the urinal!"

And for years my husband has wondered what the cats do when they roam around outside so I'm wondering if I should get him this for Christmas - or is it really a present for the cats?