Elections. As they do.
That's when people vote. And kick out a government they don't like.
Of course you could give me all the examples of liberal democracies where the government has become tyrannical against an unarmed population and abolished elections. Start with the advanced liberal democracies in Western Europe since 1945.
I would imagine, given your certainty as to how governments just cannot help themselves when faced with an unarmed population, that you can point to the governments of the United Kingdom, France, Italy, the Federal Republic of Germany, Sweden, Norway, Denmark, Finland, the Netherlands, Belgium and Luxemburg, abolished elections and started to abuse their people.
Obviously I never learned about this at school because I was educated in Britain. Clearly the government here, faced with all us un-armed numpties, abolished elections and pretended to hold them regularly just to fool us. The fact of our de facto tyranny was hidden from us by an education system which was forced to do its government's bidding and pretend that we still had the right to kick out any government we didn't like.
There were people at my university who claimed this sort of thing and told us that we were just naieve dupes of a tyrannical government only giving us the illusion of freedom. We called these paranoid delinquents communists and all thought they were crazy. Still I am sure that you james can now point out where we were going wrong all the time.
If only we'd had guns, then we would really know freedom. If only we were American and not the sub-human sub caste that we furners really are. If only... hand on heart looking mystically into the sky...