Housebreaking an adult German Shepherd rescue.?

If he never had any choice but to sit in his own feces, crate training alone may not work. They have their natural desire to be clean over-ridden in such a case. I would try an 'umbilical leash" method. You clip a 6 ft leash to his collar, and the other end to your belt, or a rope aroind your waist. That wat, you are aware of him, and can observe when he might need to go out, for example if he starts to look like he may defecate or lift his leg, and you can take him out immediately and praise him when he performs. He most likely will be able to be crated overnight, but for at least the first few nights, I'd put a large tarp between the bottom of his crate and your floor. This way, if he does have an accident, and there is 'overspray', at least your floor won't be ruined. Good luck with him, and thanks for adopting.