Macs at work - keeping them under the company's control

We are a new company who issues MacBooks to our employees. We have full MDM on our roadmap to roll out to our machines, but in the meantime, we need to make sure we are keeping our machines secure...

Yesterday, we terminated an employee - he had his iCloud account tied to his work Mac that we issued him, and it appears that he used Find My iPhone to remotely lock and wipe the machine after he was terminated.

What do we need to do on our Macs before we hand them out to avoid this kind of issue in the future? I have been administering Windows laptops for years and know all the ins and outs of MDM and security, but I'm new to Macs. Until we have a full MDM solution in place, we need to know how we can manually set up the Macs before we give them to employees to make sure we cover all of these kinds of security risks.