Uh, the only way to revenge kill garchomp is to force it to outrage. Other than that, you can scare it away....if that is ok for you. Ice shard from weavile and mammoth can ohko garchomp. Starmie can ice beam it. Aerodactyl can ice fang it. Cresselia can usually do the trick too.
Actually cresselia can just come in straight into it.
Actually cresselia can just come in straight into it.