The collars only work when you get close to the line and/if when the dog jumps over it ... voila then there are no shocks going on.
Big dogs can be real scary to people that are not knowledgeable about dogs.
This particular incident was sad and unnecessary. Dogs can not be left to run free without the owner being with them. There are businesses that use dogs as night guards at their businesses. MO.
This is a failure of the dog owner to set his system up properly. I have mine set for a 30' barrier. Also, most systems have multiple sets of prongs to use on the collar. My dog has fairly long hair so we went with the longer set. Further, she's a bit of a speed demon so she doesn't get the "warning" buzz... She just gets the ZAP. She's learned quick where those boundaries are at.