My sister-in-law has a male kitty, Wilson who is nearly 6 months old. Up until lately Wilson has had a litterbox and been an inside kitty. she wants him to go outside to do his business like her other cat Ziggy. Well, he doesn't seem to want to do that. She puts him out at regular intervals but he insists on pooping everywhere in her house, always in a different spot. He always holds his pee and does that outside. She's getting very upset at having to clean up poop all the time. By the way, he isn't ill and doesn't have worms. Any suggestions?