OK, different bureaucracies. Looks like the yard is much higher than the roadway below, and all the services are run underground(telecoms, nat gas? etc) as well as the usual underground water. Either that or there is a stormwater/wastewater or land retention feature under the dirt.

In the US, all the utility companies together sponsor a free underground locate service. They map with spraypaint where the services are, so you can excavate safely. If you knew where the services actually were, you might be able to raise your fence higher, if local codes allow it. Your fence is nice looking, and your dogs are beautiful. But Frenchies aren't that tall, and even little dogs need a taller fence than what you've got.

In the meantime, could you post a tasteful sign on the outside of the fence with your contact info, so if your dog escapes again it would help?