How are his poops? Soft, hard? Haha seems pet people spend alot of time talking about poop! Is he long haired or short?
If he's eating mostly dry food, he might be a bit constipated. I have one cat that will sometimes poop out of the litter box and I've found that it seems it happens when his poop is hard so it maybe a bit uncomfortable for him. See if you can get him to drink more water, you could add chicken juice or beef broth, without salt to his water. If chicken's not too expensive for you, you could try cooking a bit for him and see if he likes it.