Just a few ideas... Put him in the box every fifteen minutes after he eats for about an hour, he should go during that time and get the idea. If you catch him scratching or seeming like he might be looking for a place to go put him in the box, if you find feces on the floor, place it in the box and show it to him. if you catch him in the middle of urinating or defecating, spray him with water and then put him in his box. If there is a place where you usually find he's gone to the bathroom, put the litter box there, he might get the hint and start to go in the box. I hope some of these ideas work. let me know how things work out!