As simple as it sounds, have multiple people relay the GPS to the geohash. Requires planning for where to hand it over.
- The larger the group, the easier, but any group of people can complete the achievement.
- Each person must run approximately the same distance. (If impossible, adjust.)
- Only one person can reach the geohash, but if you took part in the relay, you qualify for the achievement.
- If one (or more) people qualify for another achievement (e.g., water, juggernaut), only those people can claim the achievement.
- Each person must walk the GPS to the geohash. This qualifies each person for the walk geohash. Using assisted transportation to cross an otherwise uncrossable surface, such as water or a canyon, does not invalidate the walking requirement.
 Honorable Mention: Assisted Relay
Regular proof of position is required, plus proof, and preferably coordinates, of each hand-off.
Feel free to link here, with proof.