My cat does it too. Checkers used to have his box in the basement where he would frequently hit the wall behind the uncovered box, but we didn't worry much 'cause it was just plywood and in the basement. He peed in the box sometimes, sometimes not.

Then I moved the box upstairs into my room. Same deal, sometimes in, sometimes out. Couldn't have that, so I put it in a big cardboard box--then he never peed down into the box. I think he was thrilled to have a close-by surface to spray. He liked it so much he sprayed OVER the box.

That's when the covered box came on the scene, and it works great although he never ever pees into the litter or covers it anymore. But hey--he's apparently happier spraying

Usually he wants to look out while he's doing it so it all winds up on the back wall, once or twice he's sprayed out and then it's Carpet Fresh fo Pets to the rescue--works great, i just clean up with a wet/soapy paper towel then spray it with that for the odor. It seems to get the stain out too.