The Marin Humane Society sent a frustrated letter earlier this month to the Golden Gate National Recreation Area over the proposed elimination of all but one of the park’s off-leash dog walking sites in the county. Society spokeswoman Carrie Harrington said that although it is important for pets to be under voice command, Marin’s estimated 60,000 dogs deserve an outlet for their energy. The letter called it a shame that “responsible dog guardians will be…