The biggest investments you can make in your club are your staff and yourself.
Just like our technical skills are perishable, so are teaching skills. They get better or worse, dependant on the time and development you commit.
So create a culture at your club where this is just part of what you do.
From your Leadership Team up, have a regular allocated schedule of training to develop teaching skills.
The best retention tool is to have great classes, and the best way to have great classes is to develop great teachers!