Two toilets
Have had to do this myself before when one becomes seen as a rather handy place to put a hoard! If he pees higher than the back of that tray you can get bigger ones for guinea pigs - that would double up as a sand bath/digging place as well.
So a big one and a small one in the other area? Maybe wait and see where he chooses to pee in the Barney cage
At the moment he might be changing his toilet corner for various reasons if things aren't right for him.
Someone else had this larger one , ordered by mistake. It is quite big - but she liked it anyway.
https://www.amazon.co.uk/Rosewood-Co...gateway&sr=8-3
When Newt stopped using his for a while it was to tell me he wanted it somewhere else - so I moved the toilet where he moved his pee corner to.