I'm sorry you are going through this with Kioko. I know it must be frustrating. Maybe he just gets so excited to be with the others when he goes outside. What if you keep him in an xpen or larger kennel for a while along with a puppy pad. Would you be against him being puppy pad trained? It's worth a try. No matter how hard you try, Bless his heart, he may be one of those that just likes to have his quiet time and takes longer with the pooping.
I hope it gets better.