I hadn't heard of a prong collar so looked it up and found this descriptionthey then have their pinch/prong collar that they wair for walking.
"A dog training prong collar is made of interlocking metal links. Each link has two prongs that protrude inwards. When the collar is placed over the dog’s head, the prongs sit against his neck. When the animal performs an incorrect action or pulls when being walked, the trainer corrects the behavior by tugging on the leash, which in turn causes the prong collar to tighten and pinch together the dog’s flesh."
Ouch - Is that what you use on your girls???