Dogs are, by nature, territorial creatures. This knowledge, however, is not all that comforting when your pet is incessantly urinating up the arm of your sofa to claim it as its own. Territorial marking can be a real pain and can easily reoccur if you aren't careful, so you need to take action as soon you notice it occurring.
When a dog marks something, whether it is a piece of furniture, a wall or even your leg, they are essentially saying "this is mine". In order to do this, they spray a small concentration of urine onto the object. This is just enough to make it smell like your dog, so other canines know through scent that they are in another's territory.
It is actually somewhat of a good thing that your dog is protective of you and your home. However, there are much better ways of expressing that than by spraying. Your dog is unlikely to listen to reason, so you will have to take different steps in order to prevent this behaviour.
One possible solution is to spay or neuter your pet, if you have not done so already. A lot of territorial behaviour in dogs is due to their sexual instincts, to warn potential rivals away so they can mate and to attract a partner. Removing that drive can eliminate the behaviour.
This is quite drastic, but it is effective. However, if you want to breed your dog (or at least leave it capable of doing so) then you need to take different steps. A likely cause of spraying is if your dog notices a new face and sees it as a potential intruder into their territory. This can panic them and cause them to reassert their dominance through marking.
To prevent this without neutering, you will need to introduce new visitors to your dog before you take them into your home. If your pet understands that these new people are not a threat and are friendly, they will be much less likely to spray.
Written by: Hannah Dyball