Male dogs have strong instincts to mark their home territory. If a dog perceives the boundaries of that territory to be outside the house, there's a better chance the will wish to leave these scent marks there.

Most male dogs can be overstimulated to the point that they will mark indoors. It just depends on the level of stimulation in the situation, and on the individual dog. Neutered dogs are triggered to this behavior less readily, particularly if neutered during the first year of their lives. One example of a situation that could elicit urine-marking from a dog you've never seen do it before would be if another male dog visited your home and did it first. It's highly likely your male dog would mark over that urine.

A female in heat is another stimulus. Some males will be stimulated by a cat litter box being in the house, or a baby with a dirty diaper.

Unless any old housetraining accidents from dogs living there in the past or present are neutralized by the right methods and products, these will strongly stimulate the dog to mark.

Smaller dogs tend to mark indoors more, perhaps because the inside of the house feels to them large enough to comprise a home territory. Another reason is surely that the smaller amount of urine output makes it more likely an owner will not find and properly treat a small dog's accidents. Then the scent remains and signals to the dog's instincts that "this is the place." Housetraining accidents from a larger dog are less likely to be overlooked in this manner.

Urine marking is far from hopeless. Most of all, it is NOT an insult from your dog to you. The dog is marking out the territory he's willing to lay down his life to defend.

Here are some steps to take if you are dealing with this problem:

1. When your dog has this problem, act quickly before it can become a habit.

2. Have the dog neutered as soon as your veterinarian says he is a good candidate for surgery. If you plan to keep the dog intact for breeding, realize that in some cases this will mean  your dog will never be reliable loose in your home unsupervised. It's preferable to neuter prior to the development of indoor urine marking, but later neutering may still help.

3. Confine your dog when you can't supervise him, and supervise him whenever he's loose in your home, just as you would a dog who isn't housetrained.

4. Consider the use of a belly band during the times you're supervising him in the house. This is a soft band to catch urine. It could breed infection if worn all the time, but can serve as a back up for short periods when the dog is loose in the house under your supervision. Some owners have found it helped call the dog's attention to what he was doing. This behavior is instinctive, not premeditated, and perhaps the belly band helps make it more apparent to the dog. At the least it can help prevent some accidents.

5. Don't use punishment for any housetraining problems, including this one. Even if you catch the dog in the act, simply interrupt him and take him to an approriate place for urination. Praise him when he does it there. Don't let housetraining issues of any kind ruin your relationship with your dog. In fact, handled correctly, housetraining can be one means of developing a good rapport between dog and owner.