I mean, it sounds like his concern for you using these tips out in the world at school and work. when he isn't speaking to you he seems to want you to succeed. If he isn't being cruel his concern might just be heavy on you. My parents clearly felt guilty for my stutter but not their fault. I was an early reader and I only began to stutter when I went to school and kids made fun of me so I learned to especially stutter in classroom like situations and being pushed to speak in front of a group. The only thing I can do is go easy on myself if I stutter and try to change my voice. I have volume issues sometimes because I would rather be loud than be quiet and get stuck. Anyway, when I was in speech therapy they would try to support me and they were told the techniques would work. Maybe they would have worked if I had also been taken out of the stressful classroom environment. Unfortunately that's not how public school works! I don't think it would be impossible to think of a way to tell him that you appreciate his concern but that it kind of gives you stage fright and you don't want to go on being on edge about fluency when speaking to him. I stutter most when I am gauging that I will be judged or even just noticed more. When I gave up speech therapy it took my family a while to stop doing stuff like this in an effort to help me remember. The best thing anyone ever did was give me a break and just let me work it out myself. I know not everyone has this experience so if you are still using these methods and just want him to not keep coaching you. He's your dad and he can support you without policing your speech like that even if he is doing it out of genuine concern. Good luck and keep talking it sounds like you've got some tricks. It's like a magician doesn't want other people to see how the trick works they just want people to see the result. I have the worst issues when performance anxiety is a factor maybe you do too.