My heart always goes out when I hear of bolting.

It was and (to a
very small degree) still is a problem. However, what I have started doing lately is using a small, metal and silent whistle that is tuned to my Pyppyn's "ears" and it has been very good at stopping him in his tracks and having him return to me.
I found one at Petco for about $3.00. They should be easy to find at any of the PetCo/PetSmart retailers. And you literally tune it to your pup's "frequency". Of course our limited human ears cannot hear it but my yorkie sure does.
Would like to know if anyone else tries this and what the outcome is!