My male lab is just over a 15 months old and was castrated at 10 months old. My sisters female lab is 2 years old.We walk our dogs regularly together and they started this clacking of teeth and tearing around together out of door on long walks when off their leads. It always looked like they were enjoying themselves. My dog would go for the females neck, she appears to ‘flirt’ and lick his mouth and eventually after running around together clacking their teeth for up to 20 mins at a time,they would stop,catch their breath,and start all over! They really appear to be the ‘best of friends’ and my dog follows the female everywhere. However it has now got become an absolute nuisance especially when we want them to be calm and settle in each other’s home after what is usually a 2 hour walk. It doesn’t take long for my dog to start,and the above cycle starts all over. Indoors we have tried restraining them on leashes, distracting them with balls,chews or bones which work for a bit, and using a stern ‘stop’ before we know it is about to start. It is very strange because neither dog does it with any other dog they know. Can anyone give me any advice on the beast way to stop their behaviour please.