This only works in Co-Op
The "Gold Medals" are nothing else than the Symbols in the Endscreen statistic and you need to have all on gold.(Be the best of your team)My Solution
Grab a friend or use the Gaming sessions here and to make it simple play with only 1 partner!You need to reach wave 10 and the easiest map is "Dead End".And there are 4 more requirements to be fulfilled to get the achievement:Best Shot:
The longest with the highest combo
Do a 30x combo and get a 70m long shot and you're good to go.Kills:
Get the most kills, the preacher will be helpful and the explosives too.Revives:
At round 9, leave one zombie alive (erm...) and your buddy takes the fall.
Lure the zombie away, revive and kill the zombie.
If you go down in the game, he needs to go down twice etc.Highest Combo:
Captain obvious is not in the house.
Just make sure you talk to your buddy that he doesn't get a higher combo than you.
Your end game screen should look like this to get the achievement:http://www.directupload.net/file/d/3932/9zgq6tn2_jpg.htm