Cat pooping on floor

My 16 year old cat Buster is driving me nuts as he has taken to pooping in random locations. At night I close off the living room and that seemed to help, though the last two nights he makes his poo in the box, then finishes outside the box in the hall, and last night, IN MY bedroom. The smell is a killer, and works like an alarm clock!
I took him to the vet a few months ago but there wasn't anything wrong that he could determine at that time without a lot of expensive tests. I did bring a poo sample which was fine. He was given a cortisone shot which seemed to help for a few weeks. What I notice is that he goes in the box –and then he still continues to go outside the box to finish up in another room. This appears to happen only at night. I catch him sometimes and put him back in the box while he is squeezing, and then he doesn't go in the box and runs off like a frisky kitten, its quite funny! But, in all honesty I am very concerned about this behavior. It should be noted that when this started a few months ago I bought two 2 new litter boxes with all new clumping litter (the kind they seem to like best). I clean the litter boxes every morning, and this week I have also been cleaning it before we go to bed. I am a slave to these litter boxes! I thought MAYBE he couldn't find the box at night so that is why I closed off the living room- which at least is saving my beautiful rug in there. He is finding the box at night, but not completing the task at hand. I have two cats, and this is only a problem with Buster. I have Feliway plug-ins in two rooms to lower his anxiety (he has it bad!) and I live in a small one bedroom apartment so that is the most I can use. It does calm him down a lot, I couldnâ€[emoji]8482[/emoji]t live without them. He is constantly sniffing everything -- so I think he smells other animals that must show up on my shoes so when I come home he smells it. Anyhow, DOES ANYONE HAVE ANY OTHER THOUGHTS OR IDEAS??? He's been to the vet, has new litter boxes (2) in location away from his food-- he goes poo twice a day- box is cleaned twice a day—honestly, I donâ€[emoji]8482[/emoji]t know what else to do but spend the money for the tests. My cats are my kids—love them so much and it is difficult to consider that this could simply be an old age thing—I hope it can be resolved and soon!

Poor little Buster, it could be age related, the fact that he's doing half of it in his box shows that he's not doing it intentially to be a bad boy. Someone will be along with advice for you. Good luck to you and Buster.

It is possible to do the tests one at a time so it's not such a financial problem? Or at least not have to do all of them at once.

My cat is so afraid of the vet...I have to do the one at a time routine for my kitty because she gets so scared the vet won't handle her for more than a few minutes at a time. He doesn't want her to get to the point where she won't allow anything to be done to her. It also helps me to budget for tests when they don't have to be paid for in one big lump.

I'm leaning toward it being an age issue. Maybe he's just not as sensitive as he used to be and thinks he done before he is? Is there a particular place he goes to and could you put down a puppy pad or something similar for him to finish up on?

I'm just wondering if, at his age, that he has lost some sensation back there in the pooper area and doesn't realize there is still poo there? My BF's elderly cat would sometimes come upstairs from his LB with a poo-poo still sticking out from his behind and he would inavertently drop turds elsewhere.

Or it's possible it's a mental awareness issue...

Either way - I don't have any sound advice to give you. My BF was on constant poo patrol.. after finding some in the dark with his bare foot.