What an absolutely gorgeous dog! What breed or mix is he? What are you correcting for? For breaking a heel? Or for spooking/shying away? Because the spooking is thw anxiety, correcting that involuntary emotion would seem unfair. But holding him accountable for a command he knows well to give an alternative job seems more fair and productive, over time I assume the anxiety would naturally reduce.
The extra line is a metal wire and is secured to the handler’s body with a secondary wrap around leash, this is for safety. With a dog dealing with extreme insecurity, all precautions must be taken to ensure their safety as their training progression is continued.