I also posed the following questions to my friend in Northern Ireland, but again didn't get an answer ....
If England starts producing chlorine-washed chicken and hormone-fed beef, who stops it getting into the ROI and maybe even France, where I'm guessing it would be illegal. Is there an expectation that it would never enter Northern Ireland in the first place, or would it be stopped at the border with the Republic. And if it got into ROI, what's to stop it entering France and the rest of the EU?
Asking practical questions about Northern Ireland is not often a fruitful exercise. Image and presentation are for more important than substance.
In the days when the border was reasonably 'hard', for various reasons, there were, I believe, only sixteen* legal crossing points. There was much smuggling, in both directions, even with much higher levels of 'security' than there is available now. It will be entertaining, whatever happens.
The final trade deal needs to be agreed by all 27 remaining countries - if only one feels hard-done-by under the terms of it, they can veto the whole deal.
The EU has current external land borders with many states, they may have some ideas from those.
*Edit - From a 1973 Home Office report, when they were worried about more than the odd dodgy chicken -
There are 303 miles of the border. There are 20 approved roads, 187 approved roads and 17 concession routes… The facilities for crossing the border are much greater than the number of cross-border roads. In particular there are 30 miles of water, numerous lanes and smugglers’ pads and border lands which are easily negotiable on foot.
Further edit - after 187, in the extract above, it clearly should say "
unapproved roads".