We have an extension to the take home done paired on site that usually involves significant refactoring. If you don't have a clear understanding of the code you're sunk. Plus the presentation should weed out the most egregious cheats. I also strongly suspect that developers that can't solve the task well will mainly have friends that also can't solve the task well. If someone had skilled developers invested in them doing well I suspect they are most likely a skilled developer.
> We have an extension to the take home done paired on site that usually involves significant refactoring
That sounds actually brilliant. While some might argue that this comes back to the "whiteboarding under pressure", honestly if you have already written the code from scratch you definitely should be in a much better position than with the usual "implement a red-black tree insert, you have 15 minutes" whiteboarding tasks.
