(quoted from post at 12:31:18 09/06/18) A lot depends on the dog. I have several friends who have had excellent luck with them, but the common themes are that they all have smallish well-trained dogs of reasonable intelligence and they took the time and effort to properly train the dog to know the boundaries, respect the fence, and come when called. Other friends have not had as good an experience. One friend's german shepherd was smart enough to stand in the zone where his collar would beep but not shock him until it ran the battery down, and then would take off for parts unknown. Other dogs would, as mentioned, be fine until something really grabbed their attention--a car, a cat, another dog, etc.--and off they'd go, yelping until they got the beyond the transmitter's range. Others just didn't care if they got shocked--another friend's Rottie would just wander in and out of the zone at will, and yes the collar DID shock hard enough to draw a yelp and some Very Expressive Language from the owner when they tried it to see if it was defective! He was, apparently, just too dumb to care, as he was well-behaved otherwise. Also saw a case where another friend was dog-setting and put their spare collar on the dog they were setting without thinking she'd never been trained on the fence. She wandered off, got shocked, and bit my friend when she ran to pull her back into the "safe" zone--this from an old hound who'd never hurt a flea, but, quite understandably, thought my friend was purposely hurting her and returned the favor. In short, they're no cure-all, and for it to have any chance of working you will have to take the time and trouble to properly acclimate the dog to it, and even then it may not be enough for a big dog with wanderlust.