I don't have a male, but I have a female that marks, both outdoors AND indoors.
She was potty trained completely by about 5 mo. (accidents in other people's homes when she got busy and couldn't find her pad quick enough, but VERY, VERY few accidents at home). Around the time she turned 6 mo. old, she had "accidents" ON FURNITURE, once at my house where my cats like to lay where she can't get them, and once at a friend's house where her cat likes to lay!! Right after, I got her spayed, but she still marks....especially outdoors (and she'll even mark places SHE'S pottied before
), but she'll mark inside too, especially if we're at someone else's house and they have a dog.....I don't know if she's smelling that dog's accidents or what??? She has been pad trained, but we just started (a couple of weeks ago) outdoor training, and I'm REALLY hoping that solves the majority of our problems.....because it IS a problem!!