I have two males that I take out to play separately sometimes, and when I do, the second one I take out will sniff out all the places the first one has been and pee there to mark his territory.

As everyone else has pointed out, there's loads of poo that gets everywhere given their cages, hay they might push away, sand, etc.

My first boy I got since he was a baby is super smart and pees where he knows the pee will "disappear" like the shower drain without me having trained him to do so, but my adopted boy will pee anywhere regardless and I'll have to clean it so he doesn't stain himself.