Kitty goes _outside_ the litter box... help!

Hi,

I have 2 cats, Lukey and Oreo. Lukey is older than Oreo by a couple of
years. Oreo is 2.5 years old. They've been together for almost 2 years.

Oreo has had a habit of urinating outside of the litter box. But he poops in
the litter box.

I had the litter box on the bathroom floor, and he started urinating on the
floor. This became a lot of trouble to clean up. So I moved the litter box
into the bathtub (guest bathtub, no one uses it). He still doesn't urinate
in the litterbox, but now urinates in the bathtub. A little easier to hose
down.

Why is he doing this? He poops in the litter box just fine.

I've also tried setting up TWO litterboxes, one for Oreo, one for Lukey.
That didn't solve it.

I just recently bought an extra-large huge litterbox, thinking Oreo didn't
like the smaller one. That didn't solve it.

Tried it with the litter box hood on and off. Nope.

Tried 2 different brands of litter. Nope.

My only thought on this is that sometimes I'll find litter scattered outside
of the litter box when the cats leave tracks or scoop at the litter, and
that Oreo assumes he's supposed to urinate anywhere he finds the smallest
amount of litter, even just litter paw tracks. So he pees on the litter paw
tracks.

What's going on here? And how do I correct this behavior?

Meow!
Scott,
Oreo & Lukey