[My dog] will poo about 10 minutes into the walk usually. BUT, he won’t even pee in the back! He would before we moved, but now we moved to a new place that doesn’t have the best landscaping-not great grass-and hasn’t had any dogs so it doesn’t smell doggie- the 2 things I think he likes.
He will go pee every time we walk him, which is 4 times a day right now, and he will poo twice a day.
He gets fed normally about 6AM and 6PM, with closer to 9AM on weekends.
My advice is going to suck for you since it’s gotten so cold out lately. I would leave him outside in the back for longer than you are (presuming it’s safe to do so.) Keep an eye on him (from inside is ok!) He will have to pee eventually. When he does, shower him with praise. More than you think. Be excessive.
An additional approach would be to pick up whatever he pees on during your walks. If he pees on a bush, snap off the urine soaked branch and bring it to your back yard. This could help him realize that your backyard is a bathroom, too.
Yet another option would be to ask a local doggy daycare for some of their gravel or dirt. This should smell a lot like other dogs and may help kick in his marking instincts, which you can then also reward him for.
Lastly, there are little grass pads you can buy for dogs. That would certainly be cheaper than re-landscaping your entire yard!
I think that once it clicks in his head, your problem will be gone, it’s just a matter of figuring out what small changes will turn that light bulb on above his head!