Where or how to host secret code (from hoster)?

Question

i would be very interested to know where you host websites whose code is not allowed to get out to the public. For example, I found out that big hosters in germany give their support staff full access to all files in the hosting of their clients. I assume that it is relatively easy to sneak a support job there. i am aware that the employees have signed contracts stating that they are to keep the customers' data secret. But what if a well-known website is hosted there and an employee downloads a copy and searches for weak points in the code at home to exploit them for himself? Is there any way to protect particularly sensitive (php) files from the hoster?

How do the big players do it. Do they all host on their own servers?

I am curious about your answers.