Not using litterbox

Question
I have grown up with and lived with cats for 50 years, but my current pets have me upset. I have a 12 yr old neutered male who sleeps 95% of the time. I have a 2 and 1/2 yr old neutered male and spayed female, brother and sister. Last, I have a 2 yr old half Siamese neutered male. One of these has started to poop in a corner of the living room on the carpet. It happened once last week and once this week. These are all indoor cats, front declawed. Both times it happened, I was only 15 feet away in the dining room, but sitting at the table and doing paperwork. I was alerted to what happened by the smell. I know its not the Siamese, and I doubt if it was the oldest cat. Also, within the last few weeks, the brother and sister cats have been picking on the oldest cat and chasing him and fighting, just like schoolyard bullies. Their tails puff, lots of growling and body contact and deliberate stalking. I am wondering if the brother cat may be trying to mark territory by pooping, because the location is close to the sofa where the oldest cat runs for protection. They only act like bullies late at night after everyone is fed, and once they get it out of their system, they live peacefully until the next night, and the routine starts again. The pooping incidents happen in the middle of the day. I can't tell who is responsible, because I don't know until the damage is done. I will put up with a lot, but not this. I have had a vet tell me that once a cat starts this behavior, it is very hard to stop it. Can you shed any light on why perfectly peaceful and trained cats would start the bullying and pooping in the living room? These same cats will all sleep together on my king-size bed. And up until the last 2 weeks, I had no problems with them. Any insight would be helpful. There has been no changes in their diet or general routine or in the household routine.

Answer
Pat,

Cats are so complex, there could be numerous reasons as to why they would start this behaviour.  All I can tell you is that if you put some aluminum foil in the area where they are pooping, it should deter them.  They hate the stuff!  I wish I could help you, but honestly, the feline "mind" and their behaviours sometime boggle mine!

God Bless,
Becky