How do you employ someone but stop them from taking the money and running?

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hello yahoo community! i have an idea for an application and i might need to hier a developer who lives in another country (probably USA and i am in united kingdom). I know that international can be very shady. How can I pay someone in a way that ensures that they don't just take the money and run, or vice versa, to let the employee know that i will pay them for sure?

How do you employ someone but stop them from taking the money and running?