hmm... my Allen will pee in a laundry basket or on the kid's clothes they dropped on the floor. Nowhere else. And he only does it when he feels his litter is not clean enough. I scoop twice a day. If you have more than one cat, you shold have one box per cat plus one extra. Even with my three boxes, Allen still will occasionally pee where he's not supposed to because he's being a fussy brat! I know you said you've tried everything, but some cats have different opinions on how clean their box should be. also, some cats refuse to go pee in the same box they just went poo in. And vice versa.

I wish they could talk to us and tell us what they're thinking!