Why and how can I stop my 3yr old house trained cat start pooping on the couch?

[kissy73179]

I went away for a few days ( which is normal) and left a clean litter box, food, water and a window for my indoor/outdoor cat to come and go as he pleases(this also has been done many times). When I came home , he had pooped ab 4x on my one couch cushion. I cleaned it with rug cleaner and rug shampooer, then put a vinegar spray on it, then febreezed it. When i woke this morning, he had pooped again on the couch. There isn't pee anywhere so i don't think its a medical prob. this is his 1st and only accidents in the house in 3yrs! At 1st I thought he was mad I left him for 3 days, but then he did it again when I was home. Nothing else has been changed( litter, placement of box, food, etc...) Why would my normally great, easy going cat start doing this????? And what can I do to stop him?