I have a 9 year old male rough collie

Hi there, What you're describing sounds a lot like a reaction rooted in anxiety or fear towards people he doesn't know very well. An anxious dog might bark, lunge at people, or even jump up at them as a way of trying to cope with a situation that makes him feel uncomfortable. As a first step, I would focus on preventing him from having direct contact with guests the moment they arrive. For example, putting him in a quiet room or behind a baby gate while people come in and get settled can help lower the tension. Once they're in, visitors should completely ignore him, avoiding eye contact or any attempts to pet him. Since he has already jumped up at several people and the situation is escalating, I would strongly advise working with a positive reinforcement dog trainer or a behaviourist, and perhaps mentioning it to your vet as well. Most importantly, don't try to force him to 'say hello'. The goal should be for him to learn that he can stay calm around strangers without being forced to interact with them. Best of luck, as these types of issues can take a long time to improve, but with the right management and training, you can make real progress. Maëlla