They do make doggy diapers. They make full diapers (cover all around with a tail hole) for females and belly wraps for males. If you get a full diaper, it should catch his poop. Maybe get one in advance and try it out. They make both disposable and reusable. (Example: https://www.amazon.com/SnuggEase-Washable-Dog-Diaper-XX-Large/dp/B001VMUV0U)