They're so smart and so eager to learn and want to do what makes their owner happy with them - it isn't just their physicality.
Being a working breed it might help if you get Durango a doggie backpack or even just a reflector vest so he feels he's doing some important duty when out walking. It might even help if you write something on it like "On Duty" or "In Training" or something like that so people will tend to stay away believing he's busy doing something important. Eventually you want him to face distractions, but in the beginning and maybe for awhile it will be easier for both you and him if you don't have to be bugged by other people or their dogs or their kids. That was the biggest obstacle I had with Yoshi out walking during the day time since there were always people that wanted to stop and chat, kids that wanted to pet him, etc., etc. Mostly I just find it annoying since I want to be able to relax and enjoy walking with my dog - it's our special time together where I tell him all my problems and we solve all the issues of the world and discover all the mysteries of the universe (LOL!), and I just don't like having our special time interrupted.
I think it's pretty definite that the other dog is too much of a distraction for Durango and walks should be with just him until he gets to a point where he can be trusted to behave properly. Eventually you can probably walk them both together again as long as the other dog and Durango can do the same pace. If the other dog has to go slow, maybe then you can do some walks with both and some with just Durango so he gets to go at a faster more comfortable pace for him and gets the exercise he needs but at other times still gets to do a "family" walk. I've never had more than one dog at a time, so I've never had to really think about walking them together or separately or why for either or. I can see how it makes things a lot more complicated.
If I only had a dollar for every time I'd get frustrated with some issue or was bothered by life problems or wasn't feeling well or too tired or something where I just fell off the ball on consistency I'd be rich. We're human and have other things to do in life besides being the dog's leader 24/7. Leader dogs at least have that much easier since it's their only job. Us humans get bogged down with human stuff, so we make mistakes sometimes. Just yesterday I had a whopper of a sinus headache and just couldn't be arsed to correct Yoshi for something he was doing that I didn't want him doing. I know he needed correcting, but I just couldn't deal with it pasted to the sofa feeling so crappy. Naughty beast seems to take advantage of every time I'm down and out to make mischief.
You'll get it worked out. You already know what you need to do, and that's half the battle. The rest is just applying it.
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