It seems to me that if it's Yes, they will have the best of both worlds. If their Economy grows, they will make the English very unwelcome as they seem to be doing now. If the economy nosedives, they will flock across our porous border like the rest of the world has done, make a living including Tax Credits and Child Benefits and holiday back in Scotland.
I can't see us throwing the Scots out of England or putting up a secure border.