I have 2 indoor cats (siblings 3 years old). I had a stray come to my back yard April of this year (5 months ago). I brought her into the home, took her to the vet, she was checked for disease, given her shots, and fixed (the vet estimated her age 6months at the time of surgery). She has been in my home (with my 2 house cats) since then and has always used the litter box. Approx 3 weeks ago she began urinating on furniture in the bedroom, so I locked the bedroom door. I went away and had a friend check on the cats daily. When I returned home (5 days later) she had urinated and BM in the livingroom. I have witnessed her use the litterbox during these episodes, but I dont know what caused her to start? Any suggestions?