L.A.
Learning from experience with two sons of my own I found that a gum ball machine worked GREAT! I put a gumball machine on the back of the toilet and when they would potty I rewarded them with a penny to get their own gum out of the machine. Not only did they love the gum but they loved getting to use the machine and do it themselves. Just an idea you can even try m&m's in it whatever he likes. Let me know how things go. GOOD LUCK.