Unless we are willing to go to war - there are no viable ways to prevent China from doing whatever they feel like in the territory they control. Even the tiny Iran and Cuba survived decades of sanctions.
This just seems false. There are no ways to guarantee that they won't do something, but China, like everyone else, is vulnerable to international pressure. An optimistic historic parallel to which one could look is the Helsinki Accords, where diplomatic measures far short of war wrung what turned out to be dramatic human-rights concessions from the Soviets.
And they were not binding anyway. And I can assure you that USSR and the eastern bloc didn't comply at all.
Of course, there is no such thing as a binding international agreement—a state that feels itself empowered to abrogate an agreement will do so, regardless of anything that it has signed. As you say, in the end, the only sure-fire tool of enforcement is war, and even that is not sure fire, because victory in war is not guaranteed. Nonetheless, despite the many and flagrant violations of the Helsinki Accords, it is plausible to trace the beginning of the dissolution of the Warsaw Pact directly to the accords.
There is one recent-ish historical exception: the SA Apartheid regime was brought down by the West without any land invasion.
But invasion is no guarantee either; the Indian caste system, which makes apartheid look like Sunday school, survived the British occupation.