system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do dogs decide where to pee/mark?

I understand that dogs are marking with pee to claim territory (or whatever they do—feel free to correct me) but what exactly makes one place better than another.

I’ve seen dogs start to pee and then get distracted by some other better pee spot. Are they trying to overwrite some other dog’s mark?

Is there something special about fire hydrants/walls/poles? Or is just easier to pee on something vertical?
gpt
The same way people decide what posts to comment on online - except dogs' social media is largely made of smells. The amount of information dogs can get about other dogs by smells is amazing! Leaving their own smell is like leaving their comment on a (sometimes literal) post. A fire hydrant collects a lot of smells and so becomes the place to go to get and leave that information. A tree in someone's yard is like some random dog's blog. A fire hydrant is like Facebook.