For most of the time we were doing ok. It was always a case of just managing them, they might start causing trouble, and we would use a carrot and stick to stop it. China generally did enough because they don't want the West coming in and
everyone would rather a slow path to unification rather than the entire and sudden collapse of the country.
However since Kim Jong-un they've got more antagonistic and less predictable. His father would ultimately behave with a degree of rationality and his provocations were usually a intentional attempt to extract a concession from the world. Now Kim Jong-un seems like he really does want to start a fight.
I think it would be better to leave it to China. It's entirely in Chinese interests to stop North Korea getting a missile, they understand the region and the regime better, and they have more influence. We also want to keep China onside considering we're going to have enough problems with Russia to deal with.