Porter is a surname masquerading as a first name, which is exactly what makes it work on a dog. It's in the same family as Cooper, Tucker, and Hunter: occupational surnames that have migrated into pet naming and feel confident without being pretentious.
The Occupational Surname Wave
Occupational surnames as dog names have been a consistent trend for years. Porter (meaning someone who carries loads or guards a gate) fits naturally in this group. It implies a working dog even when the animal in question has never worked a day in its life, which creates the kind of pleasant irony that makes names memorable. It suits large, athletic breeds: Labs, golden retrievers, border collies.
Sound Profile
Porter opens with a hard consonant, has two clear syllables, and ends with a strong "r", all factors that make it easy to call and easy for dogs to distinguish. It sits in the same sonic register as Crosby and Graham, both solid performers in the upscale-human-name category. The human name Porter has genuine usage as a baby name, so the crossover feels natural rather than forced.
The Case Against
Porter's main limitation is that it's part of a crowded category. If you want a surname-style name for your dog, the competition is fierce and most of the alternatives are equally strong. What Porter has over many of them is that it doesn't skew as masculine as some options — it reads as slightly more neutral, which gives it flexibility.