This not only makes these tiles less of a target (because now multiple players will avoid placing the robber there), but the robber will spend less time on those tiles because multiple players will be invested in removing it.
Another way to limit the damage done by the robber is to build settlements on tiles that are shared by other players. This not only makes these tiles less of a target (because now multiple players will avoid placing the robber there), but the robber will spend less time on those tiles because multiple players will be invested in removing it.