The same as it works at any other border.
But all of this is nonsense. The real question is whether or not we stay in the EU. It's not about rehashing the Scottish referendum. It's not about pre-empting some hypothetical problems that may or may not happen.
It reduces the debate to unbalanced fearmongering and tbh I find it sad and embarrassing in equal measure that such important discussions are regularly dumbed down to the level of a Daily Mail headline.
Twitter was and actually continues to be full of anti-Scottish sentiment, some of it encouraged by high profile figures and others by 'troll' accounts that they follow.
It's interesting because I find there is a massive difference between the conversations in RL and the conversations on social media about these issues.
Of course if you spend your time taking 'facts' from the media (rather than the relevant legislation and white papers) and your view of the debate from the school playground politics of social media, then you end up with a very different view of the issues and the level of debate than if you actually talk about it in RL.
So, I'm bowing out because this isn't the discussion I thought it was going to be and if I want to read lots of hyperbole about the EU and Scotland then at least Twitter only uses 140 characters to make its points.