Have you tried getting to the root of his lack of respect? I suggest having a one on one conversation as a peer rather than a boss. He may be going through something and he’s taking his frustrations out at the work place. He’s been with you for 10 years for a reason either he really likes the job or he’s really good. Also he may have lost interest in the job as well. But sometimes employees avoid conversations with their boss because it becomes to work related rather than just two people simply having a conversation. I can see you care and value him as an employee since you haven’t gave up on him due to his behavior but before throwing in the towel I suggest getting to the root of it. I’ve had a manager that was sending me to become one as well but a lot was going on. When I did try to tell her how I felt it went left and I ended up leaving a great paying job because I simply couldn’t deal with managements lack of communication. Feel free to give me a call if you want to ask other questions that may help get your employee back on track. :)