I can't tell you how many dogs I've seen in our local paper that are "lost" that say they have a fence collar on, so I agree if a dog is determined, nothing's going to stop it.
As far as cats are concerned. Personally I would not take the chance at all. Over many years, I've had both indoor and outdoor cats, and cats I thought were trained to stay on our property, but occasionally they did leave on adventures. One old girl in particular who never
ventured off the property one day decided to go AWOL for 4 days. We looked everywhere and could not find her at all. She was 16 y.o. at the time and I thought maybe she had died somewhere, but then she managed to drag herself altho she was very weak and tottering back to the house, immediately headed to the waterbowl and drank half of it. It was also obvious she'd had nothing to eat as well. She never really did recover completely and suffered serious kidney damage as a result and died 6 months later. The only way my 2 strictly indoor cats get outside now is in a pet stroller. They love a walk through a nearby park to see what's new and will actually get in the walker when I say "who wants to go for walkies?" Most pet stores sell them, and I find it's a good solution to give the cats some outdoor time and be safe at the same time. It's a win-win situation!