In the most recent SABR Defensive Index, published on 8/13, Arenado is seventh in the NL at third base. The reason this matters is that the SDI is 25% of the Gold Glove scoring. They won’t publish the final update of the SDI for the entire season until the GGs are announced.
Walker wasn’t listed yet, but perhaps he will for the final update. Through 8/13, the three lowest-rated NL OFs were Castellanos, Marte and Conforto.
P.S. The SDI is a measure of the number of runs saved by a player’s defensive performance over the course of a season, compared to the average defensive player at that position.