You could make them give a video presentation about their project to show that they actually know how it works, not foolproof but it helps. I think it is pretty

You could make them give a video presentation about their project to show that they actually know how it works, not foolproof but it helps. I think it is pretty much impossible to completely remove that possibility though. I've had lots of courses where the majority of my mark is assignments and projects, and I'm sure some students pay others to do it for them, and the professors just accept that as a possibility. I don't think it is worth providing a worse experience to the majority of honest students to prevent a small minority of dishonest students from cheating.