Nothing is 100%.
I've seen dogs climb 8' up into trees, and over chainlink fences.
I don't think efences are close to 100%, however its arguably as much if not more of a crime to take a dog and over its entire llife shackle it to a line every time it goes outside.
efences Do entail learning, if the owner actually understands how science works and behavior, and bothers to read instructions.
Anyone who disagrees probably missed that elementary class on Pavlov...
Here's a decent article with the pros and cons which seem reasonable:
https://www.caninejournal.com/invisible-fence-collar/
I would/will be much happier re-training my dog to learn to avoid the front yard border at a lower level, and then ramp it up so that its actually enough disincentive to get near it in the future.
Alternatively, we can restrict Sheltie/dog ownership to those who can afford to install a physical fence, or make it a crime to ever let your dog off the leash.
Keeping a dog perenially leashed whenever it is outside seems cruel and unusual treatment for an animal that was born to be free.
As an aside, I'm not sure exactly what can go wrong with the efence. Its a simple device that radiates a signal using the fence as an antenna.
At a certain distance I believe there are models that will beep, and then if the dog gets closer it will administer a light shock.
The problems most likely are due to owners who don't check the battery/operation regularly, or who train to just the level that the dog initially avoids the fence.
That level is enough for normal avoidance, however simply too low for a dog that is in an excited state.
I don't like to see any animal in pain, however we're talking low level shocks similar to one you'd get from a TENS unit off Amazon, or like licking the top of a 9v battery.
My dog has hurt himself far worse simply being a dog and doing dog things with other dogs.
This is far less in intensity and duration, while instilling a very real potential life-saving behavior modification.