NO choke chain or prong collar!!! He is still way too young. At the earliest it should be considered is 6 months but its better to wait until they're older. A puppies neck muscles are still developing and putting a collar like that on them can cause more damage than it can help.
As for stopping every minute, bring treats. Lure him where you want him to be. Start teaching him early that he can stop and sniff when you allow it but not every single time there's a scent that catches his attention.
Shasta GSD 5/5/10 CGC, ITD, TC
"Dax" Thor z vom Weberhaus BCAT CAX2 CGCA ETD HCT NCO-1 PKD-T RATI RATN RA TC TKA 3/18/2013
"Hades" Guilty vom Blutfeuer 10/26/2018
Zena GSD 6/1/03-2/16/2016
Riley GSD/BC 1/10/05-2/1/2013