Turbo got neutered @ 6 months & Momo got neutered @ a year old. Both are fully trained to go indoors in the designated spot (in the bathrooms) since we live in a condo. They do not mark indoors, I do have water bottles wrapped in pee paper so they can use it as their pee marker. It holds up the pee pad up the wall too.
When we're outside, Momo marks everything, even car tires
...but Turbo doesn't mark @ all.