>>Thank you so much for your prompt reply. I've tried giving him treats, but he just turns his head and looks the other way. He is letting me get closer to him. He will not, however, go out with me in the morning which is a problem because no one else is home. If he won't go out with me in the morning, he has to wait until the middle of the afternoon. I don't want to force him, but I don't know what else to do.
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I would try using my position to reduce pressure on him so he feels comfortable going out. It sounds like you have a fenced yard. If not, this would be a good reason to set up a small fenced area that your back door opens into. There is inexpensive, do-it-yourself fencing that works fine, such as welded wire on steel t-posts.
Assuming a fence there, what you could do is open the door, take a good look to make sure the area is safe, and then move away from the door. You may need at first to move so far that the dog is between you and the door--or even go out into the garage or front yard. Or go into the bathroom and shut the door.
If you want to make sure he does his business, I hear that webcams can be bought cheaply. You could set it where it will view him in the back yard so you could watch him out there. You can also hook something like that up to a TV, I think. I'd have to read up on how to do it, but it can be done. Or you could situate yourself to watch him through a window, or maybe a neighbor could watch.
You won't have to do this for long, once it is clear to him that you are not going to force yourself on him. Move away from him and get him to come to you when he is ready. Don't close in on him. That will just continue to backfire by making him more scared and defensive. It would be better for him to not potty in the morning than to make this problem worse. The longer it continues, the harder it will be to fix. It is important to relax the pressure on him and let him get over it as quickly as possible.
His not taking treats indicates extreme stress. Your best bet might be to get anti-anxiety medication for him from a veterinarian and have another family member administer it at first. I expect it would only be needed temporarily.
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Kathy Diamond Davis, author, "Therapy Dogs: Training Your Dog to Reach Others," 2nd edition, and the free Canine Behavior Series articles at http://www.veterinarypartner.com/Content.plx?P=SRC&S=1&SourceID=47