Likely because they need their anal glands expressed. If your dog does this consistently you should take it to the vet or at least a groomer, who can express his anal glands before it ruptures and you have to get a painful, costly and messy surgery. You can learn to express them yourself if you're not to squeemish, it's very easy.
Yes, all dogs urinate.
Urinate.
Yes.
they don't urinate on their food or drinking water
A scrape is in the ground with their feet, and a rub is on a tree with their antlers
Dogs urinate, defecate and respire, these are all forms of excretion.
no
Their bladder tells them "it's time"
Their scent.
Yes you can, such as a cat has a litterbox. Only you'll have to train it to urinate in that place.
from their urethras the same as male dogs and ALL other mamals who urinate!
The dog maybe a diabetic