Occasionally, I plug an external storage medium into my system because I want to use low-level disk tools such as dd or some partitioning tool. Automount is undesirable in that case.
To this end, I usually start GParted before I plug in the drive, as GParted somehow inhibits mounts (I can’t even mount the drive manually while GParted is running).
But I’m wondering if there's a cleaner way to tell Ubuntu "this one time, do not automount the drive I'm about to insert" – without making that behavior permanent.