[eagsalazar2]

It sounds like what you really have is a code management process problem. Remove him from commit access the repo, force him to submit PRs, review his PRs, provide feedback so he gets better but can't break things. Tell him this is "best practices" which is basically is. You could also take a less draconian approach and tell him that PRs and code reviews are required before merging. If he doesn't do that, then you can remove his commit access.

[whamlastxmas]

This would work (albeit in a demoralizing way) in corporate America. I don't think it's going to work when his cofounder also owns the code base and the OP doesn't really have a right to restrict him. This is a communication problem, not a technology one.

[eagsalazar2]

Also if your co-founder doesn't know he's, at least, a jr developer and you guys can't even talk about that, you have other major problems that if they aren't biting you in the ass in other ways now, they will.