Generation of secret-keepers
So, in Nova Scotia/Cape Breton, there seems to have been an organic phenomenon where an entire generation used Gaelic as a way to speak to other adults but keep nearby children in the dark about what was said. As a result, the number of speakers got completely decimated. In fact, our Executive Director of Gaelic Affairs had a father that was fluent, but didn't actually learn the language until his great uncle moved in with his family and taught him. Did anything similar happen on the other side of the pond?
My father and his family were fluent in Gaelic. He was a teacher (but not a Gaelic teacher). It was his first language. But back in the 60s and 70s TV (in English) was just getting going. All the children in my family (including me) rejected my father's attempts to teach us. TV was more interesting and easy. And he did not get a lot of support from elsewhere either.
Sadly there are still plenty of people I know who would like to see Gaelic wiped out altogether. They will be pleased when Lake Ness is used instead of Loch Ness (which many cannot pronounce properly).
But resistance is not futile....as Duolingo shows all too well!! ;-)
It was astoundingly effective, and that was just in the areas where Gaelic survived into living memory. I'm very much a descendant of the Outer Hebrides, and at 34 I couldn't tell you for certain that my lifespan (or even my parents' lifespan) overlap with that of a direct ancestor fluent in Gaelic.
While not a deliberate 'secret keeping' thing, it was definitely not the done thing to teach your children Gaelic. It was seen as putting them as a disadvantage (see various discussions of cultural / economic/ geographic factors). My father was taught English at school, along with all of his siblings. Among my cousins, only those who had two native Gaelic speaking parents were brought up with any Gaelic and then not always much! Thankfully, the next generation after me are trying to reverse this and many are sending their children to Gaelic medium education. I was very heartened, a couple or years ago, to hear some young teenagers in the Western Isles tell their companion that they wished she would learn more Gaelic so they didn't have to always speak English; as evidence that youngsters are keeping Gaelic community speaking alive. However, therein also lies part of the problem - any non-Gaelic speaker in the company will prompt all to switch to English.