Seriously, my Aussie will wait until like...15 minutes into a walk, and then he requires at minimum 17.5 circles just to poop. Sometimes I've gotta run out the door, or I know there's a thunderstorm incoming and he hates those. Has anybody trained their dog to do their business earlier on the walk?
Even though my dogs are adults and know what's up, I nearly always reinforce pottying outside by saying their cue as they start to go (for me, it's 'go pee' or 'go poop') and congratulating them on going. If they're just milling around not going, I can use their cues to redirect them and remind them what we're there for. It also helps if you always take them to the same spot to go potty and a different spot for walks. Then being in the potty spot will let them know they don't have all the time in the world to go. If you're just going out on walks, they may assume the walk is the primary activity and they can just potty whenever.
With our dog we take him to the same spots in the yard to "go potty". He knows what the area is for and once he is done doing his business we go for a walk. Occasionally he will go again on the walk. But doing it this way has been great for days we are in a rush to get out the house, he definitely goes faster.
Very similar to what Laura said above, positive reinforcement and a potty command is super helpful. I also use a patch of sod called a DoggieLawn and partnered it with bell training. In between walks, my pup will ring the bell if he has to potty, and will go instantly on the patch of grass.