Potty during walk failure

Anyone have any advice for getting your puppy to go to the bathroom on walks?

We live in an area that gets coyotes often and my neighbors have always warned me so late nights/early mornings I’ve always done in the yard. My puppy is 7mo (had him from shelter since 2mo) and has been amazing with going in our little front yard (in his favorite spot though…) and he used to be awesome at pooping on walks but always preferred to pee at home.

I tried praise and treats if he randomly would pee or poo on a walk, but now it’s gotten really bad. He basically refuses to poop or pee at ALL while on a leash, I’m sure he thinks he’s not supposed to.

We took him to a national park for some walking and he peed at 4am and not again until 3pm even though we were outside all day, cueing “potty”. He literally had dribbles coming out until we finally found an area we could get him off leash and he went.

I’m feeling terrible and really lost in how to help him now! He obviously is fine when he’s off leash and he always goes right after our walks but if I walk him for longer until he goes, it just never happens.