Zoom, I have seen how far the zap goes. The dogs shake in fear when the beep comes up which is well before the zap. Petunia, my puppy, went through it one time. She now will go closer to the edge then her sister, but I think they would have to take one heck of a leap to get over the fence considering they are Jack Russells. Wendy p.s. I really recommend getting the training from the fence people it is costly but AWESOME!!!!