Why do dogs lift their leg and mark territory with urine? Dog urine marking is not a bathroom training issue but rather an issue concerning a whole range of instinctive behaviors. Your dog may be fully housetrained and would not dream of peeing in the house but to a dog lifting his leg to scent mark is not the same as wanting to have a pee. We as humans tend to think of dog urine as something unpleasant but to a dog it is something of great interest. A dog leaves it's scent in urine to tell other dogs a message.