ALL CREDIT GOES TO AC OMEGA ON YOUTUBE
This achievement CAN be completed solo! You need monkey bombs, and either staminup, or the Level 2 katana (or both) to make a fast get away so you can make it to the required area before the monkey bomb explodes. This may take some trial and error, as sometimes the zombies will despawn before the monkey explodes, so try and throw it right on the edge of where the dog can reach.
Here's a video, again all credit to AC OMEGA, detailing where you should throw your monkey bombs and what route you should run to make it.