My brother had an electronic fence for his dog (neutered Brittany Spaniel) & his partner had one for his Chesapeake Bay Retriever (not neutered).
Both dogs figured out they could run through the fence & although they knew they would get shocked, they were willing to take the ‘hit’. The partner’s dog, being a stud, was highly motivated to run through the fence to find females. The partner said you could see the dog ‘steel himself’ for the shock just before he ran through the fence.
My brother’s dog was not motivated by finding females, but he was a hunting dog & was always looking for something with feathers or fur & once he figured out the shock was temporary, the fence didn’t hold him.
We had two beagle pups. Same thing...inground system. If these guys saw a squirrel two doors down, they’d rocket thru the “force field” and keep going like nothing happened.