What are some best practices for working with Contractors on new and existing projects (mainly mobile apps) to make sure that the Contractors do not clone the source code for their own game or application. Im sure that kind of behaviour is rare but still want to take steps to protect current and future IP when working with contractors on UpWork.
Currently we use Github for all source code repositories.
There is no way to prevent contractors from copying source code they're working on and using it elsewhere.
Unless you have them work in a secure building with no internet access and you strip search them and x-ray them to make sure they have not saved source code to flash drives, or made certain that none of the computers in the building have any way to copy files to external media of any type.
So, basically, no, that's not something you can physically do.
This is a matter of working with trustworthy people. And also, you need to understand that the contractors you hire are working as contractors because they want to work as contractors. They have no interest in starting a business that competes with yours.