>>I recently adopted an adult mix breed. He was neutered before he came home, but he is somewhere between 2 - 4 years old. He marks his territory constantly, however, not inside the house, and today, he marked people. I've never seen a dog mark a person before, is this common? Will he do it again? How do I get him to stop?
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You just watch him and move him on if he starts to do it--interrupt him in some way, without making a huge deal about it. It's a strong instinct that becomes habit. The habit can be changed, but takes time and repetition rather than a harsh method. This is a normal behavior and nothing to be alarmed about.
Your vigilance in helping him learn will solve it if you don't get rough and cause a worse problem from fear or defensiveness! He probably does this without thinking, and you'll just over and over bring his attention to the situation BEFORE he marks, so that he changes the habit.
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Kathy Diamond Davis, author, "Therapy Dogs: Training Your Dog to Reach Others," 2nd edition, and the free Canine Behavior Series articles at http://www.veterinarypartner.com/Content.plx?P=SRC&S=1&SourceID=47