As a matter of national policy, you’ve got to incur a heavier price on Russia for this stuff, although it will be hard for the Czechs alone to do it.
Why? Because if becoming mayor means that you’re likely to be assassinated, then your country will be sapped of all political talent overnight. You can’t let a foreign nation hold your internal affairs hostage, much less with violence.
What exactly would count as a proportionate response is beyond my level of creativity, and is left as an exercise to the reader.