Actually the Land Border between Scotland and England is shorter than the border between NI and Eire because the Scottish one is a more or less straight line and the Irish one is a dogleg. There is already a 'border' in the sea which determines what is Scottish waters and what belongs to England. This is the border that Tony Blair shifted north, overnight, to ensure that some of the oil and gas fields were now in English Waters.
SNP members are not fired up by hatred of the English people. Many members and elected representatives are English born and bred, They tend to see the inequities of the present system of government more clearly than native born Scots who have become used to accepting that no matter how they vote, the wishes of the 10 x larger electorate in England will decide who governs us, determines our budget, and has power over us, to the extent of over ruling the decisions of the Scottish Parliament, e.g. turning down requests for a 2nd referendum. I noticed recently that BJ the PM speaking in the HofC announced that "There will be substantially increased funding for every school in the Country ", when in fact the increased funding applies in England only. This kind of thing really jars, when England is casually seen as the 'whole country', with no thought for NI, Wales and Scotland.
Not to worry Gillybob - you will always be welcome here in Scotland and post Brexit, will be able to cross the border as easily as you will be able to go to Eire, France, or any other EU Country.