My 4 year old spayed cat, started wetting the carpet recently, after my 15 year old daughter moved back to my house. I also have a 3 year old neutered cat who I believe has claimed the covered sand box as his nap spot. I'm not sure what to do to rectify this. She never did this before!
If you have 2 cats it is best that you have 2 litter boxes. Cats like to have their own box. If it continues then I recommend that you bring your pet to the vet to rule out a medical problem such as a urinary tract infection. Good luck, vetcare