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. This message could be about whose territory it is, about the dog's social order or advertising mating availability. Dogs use urine marking to show their dominance or to claim something as belonging to them. Dogs with feelings of insecurity or who have separation anxiety may also mark, as territory marking builds the dog's confidence.