Is he still relatively new to you? It could be he’s still settling in and this will stop when he gets more comfortable. Especially if you’re somewhere with a bunch of crunchy leaves right now, everything is going to be distracting! And maybe you’re already doing this, but try sticking to the same route for every walk. My dogs are always a little extra crazy when we switch our routes. They have less focus on going to the bathroom and they’re way more focused on sniffing. I will also throw out the suggestion to stick to a schedule. My dogs would just be the worst without it.

Not quite the same as your situation - but I have a poop wander-er. She commits to pooping, but she walks so it’s like a trail of turds to retrace when picking up. I have stopped letting her walk far. I don’t add much tension, but I do restrict her from going further that 1-2 feet from the first drop off lol. When your guy gets distracted maybe try keeping him in the space where he started and be really boring so he has an opportunity to get back in the pooping mindset.

My girl is also a marker instead of a pee-er. Over time she’s now peeing most at the start of our walks, but then will work the rest of it out evenly through marking. If I don’t let her squat at least three times I risk her being uncomfortable and she’ll need to go out again. My best advice for this is allow your guy to do a ton of sniffing. The more he sniffs, the more likely he is to find something he needs to mark.

Sorry if this is useless and you’ve tried it all. My rescues are quirky as hell. But it’s really special when one day you’re like, wait look how much they’ve grown!! Good luck!