not using litter box
I have a few suggestions as well. Since he is a male cat, I would first of all check and make sure that he does not have a bladder infection or crystals forming. This is done by making an appointment with the Vet and having a Urinalysis performed, blood work may also be another option to rule out any other medical conditions or if pet relaxants are necessairy. Then your vet could help you from there. If it is not a medical condition then you can try the following.
If you changed the type of litter you use. Always use the same kind of litter if possible. Perfumes and some pearl type of litters can create housesoiling issues.
Add more litterboxes to you household. I would say if you have the room add at least 3.
Try a covered litterbox, or if you have a covered litterbox try uncovering it.
Scoop it at least 2 times a day.
Make sure that it is deep enough, about 2 inches.
Clean out the litterbox entirely at least once a month, wash it out and let it dry.
Place dishes that contain cat food on the areas that he is housesoiliing.
Put litterboxes in the area that he is housesoiling.
Stress may be an issue. You can try using what is called FELAWAY to help comfort the cat by using neutral smelling fermones.
These are a few suggestions I do have more, but usually these work.