Why would there be border guards? Scottish terrorists coming down south? Smuggling haggis in exchange for black pudding?
Regardless of a yes or no vote in the coming weeks will probably see no changes whatsoever, despite what is written in various tabloid newspapers. At worst I think the situation would be similar to that between Northern Ireland and Eire.
Of course there are going to be changes regarding who pays for what and what has control, but that'll be part of any negotiations between Scotland and the UK whether for independence or further devolution.
But that aside it appears we are entering the silly season for news regarding the referendum: Cameron is "begging" Scotland to stay, Milliband want a US-Mexico style, armed border, Farage probably wants Scotland to enter the EU, I have no idea what the Liberals want (and neither do they it seems), the Greens will be saying that an an Independent Scotland will cause further, irreversible global warming/cooling etc etc etc...
A referendum vote however is not binding and a 'yes' will just mean that the electorate have voted in favour of independence and not that Scotland *will* become independent.
t.
Ian