What actions have sporting federations taken to prevent podium sweeps at Olympic games?

To encourage competition, some event organizers or federations implement rules to prevent podium sweeps. At the 2008?Olympic?Games, China won all 6 medals at the singles events in Table?Tennis, across both genders. Following this, the ITTF limited each country at the Olympics to entering a maximum of two contestants per gender in the singles competition, thereby ensuring that no country could win more than 4 of the 6 medals available.