What did he get out of it? If he got nothing, then the contract is typically invalid. You can't give something of value without getting something in return (the consideration)(I'm not a lawyer)
Actually, yes, that's one of the things I'm teaching my first one. I'm also teaching logical fallacies, how to think about thinking among other thinking skills.
The best way to do it, is to not have to. The second best way, is to fail fast. I waited too long in my last startup and wasted too much time waiting for someone to carry their weight. It never gets better.
I recommend reading "The Founder's Dilemma's" to cover the other things you'll need to consider later as well prevent other, BIGGER, issues.