I suppose an interesting form of DoS protest would be to have a large group of people refuse to unlock their phones and take up all of the space in the customs holding cells.
Good luck with that, since most people crossing the border aren't asked to unlock their phones in the first place.
If you have any doubts about that, you should visit a US-Canada border crossing. The overwhelming majority of travelers are not subjected to through inspection.
To a free country? The US has lost so many cogs of its democracy... How far is the day when some US citizen (journalists, intellectuals) start begging for political asylum in countries that don't pride themselves for being free (like Russia, Iran, Thailand or just even Europe)?