Brandon Valeriano has some thoughts on how an independent Scotland might conceptualize its national security:
In March of 2015, a cry goes out in the town centre, everyone reacts quickly. Valuables are hidden underground; women and children are stored in hideaways to be kept safe until the danger is over. The sacred and expensive items in the church are removed and the priests flee – they are often the first targeted. The town moves to the defenses, but there is little that they can do to counter the oncoming scourge. The Vikings are off the coast of Scotland, again.
Given that House Windsor has decided against a name that could strike terror into the hearts of the hill-savages-beyond-the-wall, the Scottish position indeed seems relatively secure. If independence happens, this will make Scotland a remarkably interesting case study for security scholars; how do states that fundamentally face no security threats conduct security policy? The answer, most likely, is that Scotland will tend to take as models those countries it most closely resembles, although even in this context Canada and Ireland offer remarkably different defense profiles.
My guess is that if political entrepreneurs take sufficient advantage of Scottish nationalism to actually win independence, the new Scotland will feel compelled to compete with England in military terms, although the nature of this competition is far more likely to be “look how cool our new fighter is compared to the English” rather than “let’s re-fortify Hadrian’s Wall.” For these reasons, unless the Eurofighters are passed directly to the new (presumably independent) Royal Scotland Air Force, I expect that Scotland would go a different direction, opting for either the Gripen or the Rafale. This is to say nothing of the eventual disposition of the Royal Navy in case of Scottish independence, a problem that will be enormously complex and costly to work out.