increase in house soiling

My 15 year old male cat who is both an indoor/outdoor cat has been frequently urinating on furniture in the last year.  This seems to be on the increase.  It used to be a favorite spot on a rug, then several rugs, the couch and now our bed (the final straw).  We work hard to remove the smell so he does not got back to the same spot and have thrown away bedding and carpets.  He has a litter box available to him that he uses but more often he prefers to go outdoors.  He is a very easy going affectionate cat that does not seem to be distressed by anything or in any discomfort and has lived in the same house all 15 years.  The only change was the addition of an 8 year old male to our family about 2 years ago (previously there was an older female who has since passed away).  The 2 cats seem to get along fine and if this is marking, it did not start in the first year of the other cat's presence but has been now been noticably increasing in frequency.  We also feed him with food that has been recommended by our vet to help prevent urinary tract problems.

We love our cat and want him to live out his old age with us, but having the smell of urine surrounding us and destroying our furniture has put us at our wits end.

Any ideas what might be causing this and what to do about it?

You should probably take him to the vet. Doesn't make sense for a 15-year-old cat to suddenly start peeing on furniture unless there's something wrong with him.

I agree with the vet visit. There are several medical reasons including FLUTD and diabetes that could be causing this. Feeding a urinary food is no guarantee since there are several different causes, only one of which is addressed by the urinary foods.

Could it be when cats get old that they can't control their bladders and just let go (just as geriatric people do?)

Get him to the vet. If you let this go unchecked you could end up with a dead cat.  Any time you have a cat going outside the litter box or straining to pee, I consider it a minor emergency and the cat should go to the vet within 24 hours.  If he can't pee at all, he needs to go in right away!   He could have crystals or an infection started, diabetes, chronic renal failure....  He needs a urinalysis, a CBC and testing to check his kidney function given his age.

The longer you let the urinary issue go on for, the harder it is to treat.

It sounds like a behavior problem if he is healthy and doesn't have a bladder infection, or diabetes! My vet told me one litter box per cat, they go better with two boxes! I had 5 cats, and 5 litter boxes! I had a cat that sprayed after he was neutered, 15% of cats will continue that behavior after they are neutered! I bet your old cat is reacting to the new cat in the house. I have another male that sprays, he was recently neutered 2 weeks ago, he is still spraying :frusty: I have a full male dog that marks everything including our pillows on the bed when he is locked up in the bedroom, he is punishing us! My 10 year old cat died last year, he was the one who sprayed his whole life even after I had him fixed, well he punished me for bringing home a new dog! He finally quit once he got used to the new dog being there! When I brought in 7 baby kittens that I saved, he went on a spraying spree! He was was just beginning on being sick, so he continued spraying even after we moved 900 miles away from home.

It sounds like a behavior problem if he is healthy and doesn't have a bladder infection, or diabetes! My vet told me one litter box per cat, they go better with two boxes! I had 5 cats, and 5 litter boxes! I had a cat that sprayed after he was neutered, 15% of cats will continue that behavior after they are neutered! I bet your old cat is reacting to the new cat in the house. I have another male that sprays, he was recently neutered 2 weeks ago, he is still spraying :frusty: I have a full male dog that marks everything including our pillows on the bed when he is locked up in the bedroom, he is punishing us! My 10 year old cat died last year, he was the one who sprayed his whole life even after I had him fixed, well he punished me for bringing home a new dog! He finally quit once he got used to the new dog being there! When I brought in 7 baby kittens that I saved, he went on a spraying spree! He was was just beginning on being sick, so he continued spraying even after we moved 900 miles away from home.