Hi, Ellen. I've had Greys for 7 years now. I've NEVER run into anything like this before. You said you've had this dog for 3 years and he's 6 years old, but he's never demonstrated this behavior before. Robert mentioned some sort of medical problem. Usually, my first instinct with housebreaking issues is a UTI (urinary tract infection), but that sounds unlikely if he just doesn't want to go outside.
Has anything in your yard changed in the past month? Anything out there that might have spooked him? One of my pack won't go out after dark. But he's afraid of a whole list of things.
Are there steps going out to the yard? Is it possible he's got arthritis and it hurts him to go up and down the stairs?
Is he shy or scared around the door? All doors or only a specific one?
How does he act once you get him outside?
Does he hold it throughout the day and then only goes out in the afternoon when you get home?
Is he having trouble lifting his leg to pee? That could indicate a back or spinal issue.
Is he still running? Any limping?
You might try posting a query at
http://www.greytalk.com. I bet there's someone on Greytalk who's run into this situation before.
Feel free to PM me or send me an email if you want to chat about this further.
Lois