@oshizu cats everywhere are pleased they don't have to be trained
and get the catnip too! But let's be honest, the dogs love the process and get walks. I wanted to walk a cat and teach it to go in the toilet though.
One Playalot told me that I didn't consider at the time was that you can basically be your own vet at home and save time if you're willing to study the skill and buy the equipement (from pets menu under sort by function). Your dog might not like it short-term but long term you'll come up with some great treats for him by practicing.
Cheats this time around are major_veterinarian 10 and stats.set_skill_level skill_dogtraining 5 for pet training. Which really might as well be dog training yeah.
You can adopt ghost pets at brindleton bay cemetery, north of the lighthouse/museum in the woods near the rocky area. You can become good friends (the required level to invite to household) with less than 6 interactions with the animal.
Everyone's probably heard of Mayor Whiskers, the stray who wanders town that can be adopted, but that's another one not mentioned yet.