Rescued Adult Dog Pees in Crate When Left Alone?

We adopted Joey about 5 months ago after our other Boston Terrier passed away. (We had disposed of all of the previous dog's belongings, and there were zero accidents in the house from the previous dog).

Joey is a 6-7 year old adult, and we adopted him from a Boston Terrier Rescue in another state. They had picked him up as a stray, which they believe he was for a while as he was covered in fleas and very dirty. We believe he spent most I his life (before they rescued him) in a breeder/puppy mill situation. It's impossible to know for sure.

He is a very sweet, affectionate, and appreciative dog, as he was when we first visited him at the rescue shelter. They neutered him just before we picked him up. We are retired so the only time he is alone, may be for 3-4 hours when if we have something to do and cannot bring him with. We take him everywhere we can, as he loves car rides, and is even comfortable staying in the car while we run errands (weather permitting, of course.) We live in Minnesota for most if the year, but winter in Mesa, Arizona.

He made the trip with us to Arizona (flew first class without any issues at all) and adjusted to our home here with no other issues. (This issue has been consistent in MN and AZ). He gets taken outside frequently, and we keep him on a very regular feeding and bathroom schedule.

When we go to bed at night, be goes in his crate, and is perfectly fine. But when we have to leave him during the day for any amount of time (he goes in his crate as well) he pees either in his crate, or lifts his leg and pees out of the crate all over the floor, every single time. It doesn't matter if we are gone for 10 minutes or 2 hours.

We took him to the vet when we first got him and he was having this issue, as we thought it was an adjusting period, or he just had separation anxiety because he may have been left alone for long periods of time in his previous years. The vet prescribed Valium. It worked for about 2-3 occasions, but now, he just takes it, gets a little drowsy, but that's it. He is still peeing.

We don't make a big deal about leaving, or fuss when we return, as the vet recommended we try this to keep Joey calm. His crate has his blankets, chew bones, a toy or two, and we've recently started trying using a Kong with some dog food and even a little peanut butter on top to keep him busy/distracted. Still not working.

We love him dearly and are so happy we can make the remaining years if his life wonderful, but we just don't know how to fix this issue to help him? And to help us from having to clean up the messes every time.

What can we do or try? Anything is helpful!

By Kate