Accept that the Crimea was an incredibly low-hanging fruit which fell into Russia's hands for almost no effort - for a good reason.

Next, re-establish and reinforce an international climate in which aggressions are prohibited effectively - including the Westerners.


The U.S., the UK, Israel and France have become much too casual in bombing or invading foreign countries under pretences which wouldn't (and don't) pass in the UNSC (and wouldn't so even if Russia and the PRC had no veto privilege).

Estonia has ratified a treaty called the "North Atlantic Treaty" in 2004. The invasion of Iraq 2002 was a clear violation of this treaty.
Do you expect the government of Estonia to protest loudly and try to inflict some pain (such as kicking out some diplomats and CIA spies) once the U.S. president decides to casually bomb a country with cruise missiles the next time?
If not, Estonia would have little moral right to expect a less troubling neighbourhood.
Don't expect an unfriendly great power to be restricted by the rule of law if you side with great powers who de facto claim that only rule of force applies to them.