I keep coming back to this. I went on leave for a month and was concerned about interrupting some of the pronunciation courses. One client in particular was struggling with physically pronouncing many of the sounds. He works in a large public education school and needs to improve his pronunciation for obvious reasons. Before I left, we made many audio and video files of pronunciation drills. He diligently practised them for a month and I was pleasantly surprised on my return. He still has a long way to go but there was some progression and his speech is definitely clearer.
In retrospect the time off was a bonus. Pronunciation change needs time as well as practice. Change is not going to happen over night.
I am very pleased with my client's progress and his confidence has taken a boost.