__What do you do when you just can't finish a booking__?

I am currently watching a 7 month old German Shepard. I did a meet and greet with his owner and we talked about all the details (good with dogs, good with kids, potty/ crate trained, aggression habits if any, etc.) At the meet and greet, I had no problems with him, even had the owner step out to see if he and I would get along, then let the dogs do the same. Everything seemed okay, everyone got along fine. Well now I've only had him two nights and he's already bit me once, peed in the house once, and poo'ed in the house once. He constantly whines, whether he's in his crate (bed time), around me, alone, or with other dogs. Ive of course, made sure he wasn't thirsty or hungry and he's had plenty of time outside as I am home all day with them. And after these two days, I've decided he's honestly just a little too big for my little dogs.

I have him booked until December 6th, with the owner being in and out of town during the stay. How do I let him know that its just not going well and we need to find him another arrangement?