Using server-side encryption at all means admins can get into your data, does it not? They can modify the source code so that when the server decrypts/encrypts

Using server-side encryption at all means admins can get into your data, does it not? They can modify the source code so that when the server decrypts/encrypts the data at your request, it also saves a copy in cleartext. How would you avoid this without encrypting on the client side?