Cat peeing on toys!

[FuzzzyDuckosaurus]

I have 2 fixed male cats approx 7 years old. Dd is 10 months. One cat from the start didn't get on with her. The first month he was peeing on all her clothes, bedding etc. turned out he had a uti and was treated with anti biotics, lots of extra water added to wet food etc. used one of those plugin diffusers and after a month, all was well again.
Just came into living room this morning and noticed that the blanket that is on floor covered with dds toys has been peed on, several times!! I'm so angry with them (or whatever one it was!). But why would they do this now after being fine for 9 months? They are very good with her, but do tend to keep out her way. Litter box is cleaned regularly so I don't think am issue there. They are both indoor cats due to living in a flat. I'm hoping this is just a one off, anyone have any ideas?
Thanks :)