Hi, I have 4 year old male West Highland Terrier we've had since being a puppy. He used to get on well with the 3 year old male German shepherd next door. We've recently put a new fence up and the neighbours have had a new baby. The dogs now both run to the fence if both outside, growling and barking aggressively at each other and headbutting the fence, which will give way soon, I'm sure. Can anyone please help me understand what is going on for the dogs and how can we help them be friends again? Thank you.