You missunderstood what both i and
@mrbit said.
You dont train the same person to do everything, you train different people to do different parts and piece it together. Even better automate some of it, so no people.
To give you an example i have a ppc agency.
Our usp is we have a very nifty way of instantly building lookalike audiences of thousands, within 24 hours for 0 ad costs. Apply that to your ad campaign and watch roi rocket.
I have staff who manage paid ad campaigns etc, but i dont teach them how to build the lookalike audience.
So, who gives a shit if they get another job, or setup on their own they cannot take my usp with them, they dont know how i do it. Infact i actually work with lots of ex-employees who set up on their own, i actually encourage them to do it.
That is what you need to do.