We should ask a few questions to get to the underlying problem here. First, it is advisable to rule-out a bladder infection. A urine sample and visit to your veterinarian will help do that. Another biological cause of missing the box is difficulty pooping. Really, hard, dry poo (constipation)makes a kitty’s bottom hurt – once a cat associates pain with the litter box, the pain has to be fixed; then deal with the litter box aversion. Dry food makes dry cats – cats are almost pure carnivores, they really need to eat meat, meat and meat, with a few other nutrients. If the kitty is eating dry food with pretty colors, the corn and dyes are making for a dry kitty cat – try really hard to switch your kitty to moist food, canned, or preferably, a balanced human-grade meat diet, raw is fabulous!! Cats are tough- be patient. A meat-based diet will help tons with the bladder infection risk and the constipation risk.
Next, figure out if anything changed – many cats don’t do well with change – new litter, different detergent to clean the box, household visitors, new cat, dog, baby or furniture, anything different. Nighttime accidents suggest not being able to see or remember where the box is – things to evaluate at a health visit to your veterinarian. How many cats in the house? Rule of thumb is one more box than number of cats – 6 cats=seven litter boxes!! And, they should be in different places, in case there is an obstacle – like a feisty kid or puppy.
Clean the accident spots – and, boy, there are a lot of old wives’ tales about what takes out cat urine. Cat urine has fat and protein components that make it smell. A soapy bucket with laundry detergent will break up the fat, rubbing alcohol will denature the fat. Blot the area and dry. To be sure all remnants of urine are gone, use a black light – if it glows, there are still urine remains to clean. Once clean, stick the litter box right there where the accidents were happening.
Next? Confine your kitty to a small space, like the bathroom, until all potty event are making it in the box. There are also herbal cat box attractants you can put in the litter box to help your kitty go in the right place.
Here’s one final thought – I have a big boy named Kolty – he’s a big, 18 pounder, big boy, not fat, big boy. Kolty has problems getting his long body in the box and getting a good hunch, especially at night. He was missing the box, but his urine was right outside/underneath the box. Being such a big man, he needed to be adjusted, gravity was working harder on him than some of the others. After 4 chiropractic treatments, my big boy keeps his tinkle in the box.