Should our walks be focused on fun or discipline?

Hi guys,

We have an 11 week old GSD pup, our first pup ever. So far everything is fine, we knew what we were getting into in terms of work and hours we need to invest each day.

The only issue we have currently is that when we go for walks it seems like whenever we let him do his thing to make it fun for him it's literally just eating and chewing everything he comes across, wether it be rocks, sticks but most imortantly manure. We live close to a livestock farm and agriculture fields and the roads we walk on are often full of manure leftovers and our pup will grab and eat every piece he can get.

The problem is that we think this might be quite dangerous, certainly in bigger amounts, same with sticks and stones when he might swallow them by accident.

On the other hand, when we keep him from doing all these things, he will literally start whining and sitting down and refuse to walk (except when we turn around to go back home, then he will grab his leash and start running towards home right away).

We're likely misunderstanding these signals but to us it seems like if we allow him to do what he wants while walking and make it fun he will walk for as long as he can whereas if we try and train him to leave stuff alone etc he will want to stop walking and go back home asap.

Tl, dr: Should we let our pup just do his thing on walks to make it more fun or focus on discipline and training during these walks?