Of course it hurts him and chokes him.Two suggestions for you:#1 more off leash time to go at his own pace as opposed to plodding along at a human pace.
#2 stop him immediately when he begins the unwanted behavior,don't allow it to escalate.A prong collar is actually more humane than a martingale.It tightens evenly around the neck and doesn't choke.
Samson Blk/Slvr GSD. RN
Misty Husky Mix
Devo Yorkie Mix
Dakota Wht GSD at the bridge