"There are over 200 roads that cross the border."
If you have some free time, have a look along the border in satellite view on Google maps - there's some absolute beauties, especially around Fermanagh. There's farm buildings with one half on either side of the border. There's houses that are in Ireland, but the gate at the end of their driveway is in the UK. There's a main road that crosses the border four times in twelve miles. There's virtual enclaves, where sections of Ireland can only be reached by driving along a UK road (something which presents some difficulty when it comes to policing even in the current relaxed state of affairs).