No Deal it is, then. :rubshands:

[Burney]

So we would exercise our control of our border by not having a border? That makes a lot of sense

And how do you go about enforcing an immigration law without a border?

I believe others have considered some sort of wall in similar scenarios....

First, you prevent them coming by making it not worth their while - no rights to employment, housing, welfare or health provision, etc, etc (as we'll be free to do when not in the EU). They'll soon fùck off back to the Republic - and if they don't, you physically deport them.
Also, you can impose stringent identity checks on such migrants to tell you who is or isn't in your country and severely limit their rights. They can also be prevented from travelling from NI to the mainland (as we used to with certain people during the Troubles).