I have an almost 16-year-old cat who, for the last few months, has been defecating outside of her box. At first, it was just right outside of it, and then it was in random spots in the house. Recently it’s increased in frequency, and she’s also started urinating outside the box. She is urinating on the couch and in the bed. I took her to the vet and had a physical examination as well as a fecal urinalysis test and a full blood work panel. She is healthy as a horse with no medical issues and no signs of arthritis or anything like that. The vet says it seems behavioral for whatever reason. It seems like because she keeps choosing to go on soft padded furniture like the couch or the bed that she has an inversion to the litter. I have used the same litter for years, so I’m not sure why all of the sudden she doesn’t like it. Does anybody have any tips and tricks to get her to use the litter box again? I always make sure it’s clean every single day. The poop was one thing, but the urinating is a whole another ball game. I can’t keep lying down in my bed only to discover that there is cat pee everywhere. It’s exhausting. How can I get her to go in the litter box again? Is there anybody who had a cat similar to this who needed to change their type of litter? What kind of litter did you change to? What kind of deterrence are helpful? We did move recently, but these issues started months before anything changed in her life. So I know that it’s not due to any stressors. She just, for some reason has gone from being a perfect cat to not liking her litter box anymore. Please help!
Could be issues where she can’t control herself or arthritis that she can’t get into the box to use it.
Following, going through the same thing!!
I had to move the liter box in a different spot in my house. When my cat was about 17 she decided she didn’t want to use stairs anymore (clean bill of health from the vet ) so I moved the liter box upstairs, and she started using her liter box again
Have you changed the box I just recently got my 3 babies a new bigger litter box because I got a 3rd cat who is a kitten I’m having trouble getting them to use the new box
Hifzul-Rahmaan Dhansay
We had this problem and honestly once a cat peed in a spot it has their sent for ages.
My mom has one place a barn cat peed in her house when I was a child that any animal that is in the house will pee in the same spot 
When I had cats I would also when I went to work leave a “piddle pad” in the hallway incase the box became too soiled for their liking while I was it work.
Try white vinegar to clean the spots, let it set for a few minutes. I did this when litter training kittens
It sounds like in her old age she’s decided she doesn’t like the feel of her kitty litter anymore. I’d try switching her litter to softer material, try a couple different ones in different litter boxes around the house. Show her where each one is. She won’t forget if you show her once so if she doesn’t use it she still doesn’t like it. They do make pellets, and wood shavings and such. And if you can keep on top if it, you can try the paper Guinea pig shavings. It won’t help much with smell so itd have to be changed often, but itll be easier to clean than rugs and such and much softer on her feet. I have a lot of experience working in a “no kill” animal shelter, and my job was with the cats so if youd like to private message me with any questions feel free to.
Try getting a cat pheromone wall plug in for where she is most often. If it’s a covered litter box try taking the cover off. Try and find a wide and long litter box that is shorter (even a plastic tote from target without the lid).
We had this issue… this litter solved the problem have not had any accidents since changing to this. Got at petco and it is somewhat expensive and unfortunately doesn’t come in lightweight but whatever works!
Cats do this when older and it can be behavioral. As well as just loss of bladder control. 
I had to put my 16 yr old cat down because of this.
Our cats ended up on prozac because of this, they determined it was an anxiety issue. Feliway spray is a great deterrent we used. We also added more litter boxes to the house so the cats were always closer to one and had more of a choice where to go.
Get kitten attract litter. That may help as it has pheromones in it to encourage using the cat box. Also try CBD for pets to calm any nerves or behavioral issues that may be contributing. Extractlabs.com has amazing cbd for pets that works amazingly well on my cat.
Change the litter to something soft they have products made for declawed cats because it hurts them to bad to stand on normal litter plus hydrogen peroxide and baking soda is the best way to get the smell out
Is she declawed if soo this happens often with cats try a nonclay litter like paper pellets
Is she declawed?
If she is, the litter could be starting to her hurt paws in her older age
I had this issue as well … nothing I did would make him use the litter any more so I put down the puppy pee pads in a few areas, he would use them. Not the most slightly thing but at least he stopped peeing on the carpets and furniture 
When my cat got older I had to make her a litter box with a lower door. I modeled it after this one but used a smaller 18 gallon Rubbermaid bin because she was my only cat. Heat the plastic with a hair dryer to make it easier to cut and sand the edges because they can be sharp. I love Dr. Elsey’s regular litter and the Cat Attract has good reviews or you can buy the Cat Attract additive. Definitely use a sand-like scoopable litter not the crystals because the scoopable is softer. Feliway diffusers may help calm her. You could add more litter boxes because she may be having difficulty getting to the box in time or having a hard time remembering how to get to the box due to senility. Good luck. 
This recipe works better than any commercial product for cleaning pet urine. I used it on my mattress twice when my old cat had accidents and on the carpet with my boyfriend’s dog. Sweep the baking soda up before vacuuming because large amounts of baking soda will ruin your vacuum.
Try shredded newspaper in her litter box
My cat was doing that but they found a stone in her bladder