We have a male Chihuahua mix who is still intact (at least for now) who doesn't mark in the house. We were planning on getting him neutered as a puppy, but since we have not had a problem with him, we've put it off for now. All of our females are spayed, so it's not much of a problem.
I've read a lot of things about how neutering too early can predispose a dog to joint problems, since the growth plates take longer to close. I somewhat wish I waited with Cuddles, but I wasn't aware of this at the time. She seems rather long for a chi, and I've been wondering if that's why.
According to this article, "Spayed/neutered dogs are greater than three times more likely to suffer from patellar luxation".
Spay Neuter And Joint Disease