Originally Posted by Momofmany
Welcome to TCS!!
How many litter boxes do you have and how often do you clean them? At 9 months old he is gaining maturity quickly and is acquiring mature likes/dislikes and habits. Some cats will not pee and poop in the same box - it has to do with territorial issues they have in the wild (thus my point on maturing). The rule of thumb is 1 box per cat plus 1 extra. If you aren't keeping your box(es) as clean as he would like, that would also drive him to going outside of them. If you don't have 2 boxes and don't clean them daily, start there. If you are already doing this, then suspect that there may be something physically wrong with him. The only time I've had a cat poop outside the box was when he was ill. When you are doing everything right with the boxes and they go outside, always look for physical problems first.
The first necessities are to keep the litter box clean, clean up after cleaning (don't leave cleaning product residues).....Have you changed anything that would directly effect him, is there anything that may be causing him stress, house guests, construction, any sudden change in the home?