Just press and hold the buttons on both sides. Remember that. Try it now. Don’t just memorize it, internalize it, so that you’ll be able to do it without much thought while under duress, like if you’re confronted by a police officer. Remember to do this every time you’re separated from your phone, like when going through the magnetometer at any security checkpoint, especially airports. As soon as you see a metal detector ahead of you, you should think, “Hard-lock my iPhone”.
The second thing is to know your rights. Never ever hand your phone to a cop or anyone vaguely cop-like, like the rent-a-cops working for TSA. If they tell you that you must, refuse. They can and will lie to you about this. If you really need to hand it over, they’ll take it from you. And they won’t get anything from it, because you’ll have already hard-locked it, and you’ll know that you cannot be required to give them your passcode.
[Nothing to add. Well maybe… drill at dinner once a month until it has set in for the whole family? Just a thought. We did last night.]