shads

Hi everyone, Ive joined the forum as I have a very specific problem. My neighbour got a new dog about a week ago and as usual, dogs being dogs, they barked at each other and weren't too nice to each other. I put chicken wire against the fence on my side to deter my dog from digging under the fence. Unfortunately their dog dug a hole and got its head under the fence and my dog has attacked it. Who is at fault? who is responsible for costs? Any advice would be appreciated. Thanks in advance