I have one box...always have. Maybe we'll try two just to see.
I'll pick up 2 open top ones tonight along with Nature's Miracle.
Vet as soon as I get a day off
Having gone though medial problems that lead to cat pee issues, you really need to take your cat to the vet and get a workup.
Also, don't buy a litterbox, they are overly expensive, buy a plastic storage bin, they are cheap, with higher sides, effective, and can even be much larger.
a 7.00 rubbermaid storage bin is the same size as a 40.00 litterbox from petsmart. I have a cat that as she got older started peeing on top of the pile of litter and not in the hole she dug. This led to peeing out of the box, so I got a big high wall storage container and did this.
The whole was made by taping a 8x11 sheet of paper on the box and using a handsaw with a very fine tooth blade to make the cuts. I then used a hand file to file down a few sharp spots. Took 15 minutes and saved me $33.00. It's about 5 and 1/2 inches high at the bottom of the cut with 3 inches of litter. The cats love it.
If the vet tells you that your cat has crystals in it's urine, before trying their expensive food, try just switching your cat to all can food. The added water will dilute the urine and in many cases will solve the problem.
Also peeing on vertical surfaces is different than peeing on the floor. Has anything changed? Is your cat fixed? Any new stresses or changes in the routine?