It is not about being properly introduced, it is about what is around when the shock is delivered because even "properly introduced and trained" dogs have been documented to make negative associations with things in the environment near them when the shock is delivered. There are trainers all over this country whose primary business has become to rehab dogs whose owners use invisible fences. Some of those owners didn't train their dogs properly and that contributed to the issues but some spent big bucks to hire professionals to do the training and still ended up with huge issues with their dogs because of the invisible fence.
O.K we will have to agree to disagree.
"documented to make negative associations with things in the environment near them when the shock is delivered"
Documented by who? Who witnessed the training, the "association", etc. I am always suspicious of generalized comments. You can prove pretty much whatever you want with statistics. (perhaps those would have been problem dogs no matter whether they ever experienced shock or not?) You can also not go by results in a lab, because in the real world there are way too many variables to control. With invisible fence, if the dog is trained correctly it never experiences shock after the initial training, since the collars typically supply a "tone" or "vibration" when the dog is getting close to the fence. Most dogs heed the warning signal, thereby not experiencing shock again. Some dogs learn they can run through it…...a momentarily unpleasant feeling.....but again, it isn't a matter of not knowing they will get a jolt.
"Shock" training sounds nasty, but it works because most of us do not enjoy the sensation and try to avoid it. I hate getting zapped by my electric fence. My neighbour, OTOH, will touch it to make sure it is on! Not me. If I touch it accidentally, I mutter obscene words under my breath, but I don't really feel like biting anyone......nor do my horses, or any dog I have yet met.
BTW, "Professional" means you got paid, it doesn't necessarily mean you know what you are doing!