I think there should be a type of "claim" that prevents other people from placing a claim but allows anyone to do anything else as if there were no claim there. This could be used to ensure that certain areas or paths remain available for passage and to prevent griefing by way of placing claims.
Since this guarantees that people can move through an area, it should probably be exempt from the normal restrictions on how close claims can be to one another.
Edit to clarify: Basically an enforced public area.