I have a question about my 8 month old lab mix, Marley. Marley is a very energetic, but friendly puppy. She has been going to a dog park and doggy daycare since she was very young. She plays very well with other dogs. The other day 2 dogs were being walked on our sidewalk and the owner asked if they could say "Hi" to Marley. I noticed that Marley's hackles went up when these dogs got close to her. She let them smell her but then she barked at them and showed her teeth. I've never seen Marley's hackles go up before. I just told Marley to "leave it" and I told Marley to sit at my side. Is this normal behavior for a dog? I'm wondering if it was because the dogs were on her property. I'm not really concerned but curious.