Ice,
The only ex-defender I've ever met was a Polish gentleman I know who was one of the troops stationed around Findo Gask airfield in Perthshire.
Pillboxes etc would have been manned either by regular troops, or Home Guard. There's probably more chance of tracing an ex-HG than a regular, because at least some of the HG would have remained in the area for the duration. As far as the coastal artillery batteries in Fife go, there were several coast artillery units of the Territorial Army who manned them until late in the war, when they would have been replaced by HG.
I would like to have a go at contacting ex-wartime members of these units, but it's trying to find the
time unfortunately.
I have an acquaintance who interviewed
hundreds of ex-RAF personnel who manned the various wartime radar stations in Scotland/NE England. He spent
years doing it though.