I really really feel for you, I had lots of problems when I brought Odie home at 8 weeks old, up until he was 20 weeks old. I realise he was only a pup but every time I left him (5 mins or 1 hour) he'd wee and poo all over and smear it everywhere (he was in a puppy pen). This happened twice a day for 11 weeks so I can't imagine dealing with it for any longer than I did
It was a long, hard slog but I learned so much after I got some excellent advice and spent a week following this to the letter (using a crate). It involved lots of repetition and praise and helped him understand I was coming back and reduced the separation anxiety he had. He can now be left up to 4 hours with no problems

(we still have him in a crate in the kitchen, but it's a huge 48" so plenty of room).
I can pm the info I got if you'd like, just let me know. Good luck. Lesley x