- You need to be level 27 or over, have Ron unlocked for Jobs and also have a Buzzard.
- In terms of physical equipment you’ll need a rubber band, a coin and a wired controller (for most efficiency/ease).
- Call Ron and request a Job from him.
- You need to get the Job called “Base Invaders” and set the difficulty to hard.
- As soon as the Job starts call up Pegasus and get them to send your Buzzard.
- Once you get your Buzzard fly to Ron’s plane, get inside it, then get back out and go back into your Buzzard.
- Now fly to Fort Zancudo and land your Buzzard on the blue crates near the hangar that says “Zancudo Airbase” (see first image below).
- Hold down A (Xbox 360) or X (PS3) and you should continuously fire rockets at the enemy, which will keep on respawning and getting killed.
- You can now setup your rubber band and coin to keep on firing and then walk away (see second image below) – just make sure you controller is plugged in.
Full credit to Tackett79 of Reddit for discovering this!