> A lot of large companies have policies that anything you make in your off time is owned by them.

And that's just wrong, plain and simple. There's no excuse this is allowed.

> I can see why they do it my company has probably spent thousands on training and employee development and they want the return.

Training someone is not a valid claim to all uses of those skills; off-time is off-time. Just because someone applies a skill they learned at work in their off-time in no way justifies the company owing that work.