There are several reasons, both behavioral and medical, that dogs pee in the bed. Some of these include:
Marking
Some dogs will urinate in areas to mark their territory from other animals (and sometimes other humans), but when they start doing it indoors it can be a problem for you. In fact, your dog may actually be marking you because it is your bed. Many male dogs will mark things that they consider to be their property and yes, this includes you. So, they will mark things that contain your scent such as your bed.
No Access to Outdoors
If you leave your dog alone too long and he really has to go, he will. Urinating in your bed may be his way of letting you know that you did not let him out when he needed to go.
Drinking Too Much Water
Sometimes, dogs drink more water than usual. This may be from eating something with excess salt (sodium) or from a medical condition. When it is hot outside and he has been outdoors, he may come inside and drink a lot more water than he usually does, and this can cause him to accidentally wet the bed.
Excitement
When dogs get excited some of them seem to lose control of many things, including their bladder. If your dog is young, this behavior may relent with time.
Fear or Anxiety
Some dogs get so nervous or scared that they will lose control of their bladder no matter where they are. If they just happen to be hiding in your bed at the time, they will pee in your bed.
Improper House Training
If your dog was never properly house trained, you will need to start over from scratch. This can happen to a puppy or even a dog who is already trained if they are moved to a new house. You will most likely need to retrain your dog.
Medical Conditions
Genetics may play a part. Breeds predisposed to these types of accidents are the Labrador and Golden Retrievers, Siberian Huskies, and English Bulldogs.
Diabetes is a disease caused by the pancreas not producing enough insulin and happens in one out of every 500 dogs. Other signs include weight loss, excessive thirst, vomiting, and lethargy.
Urinary tract infections are one of the most common reasons for peeing the bed in dogs. Females are more susceptible than males, but both can include signs of increased body temperature, general ill appearance, lethargy, and excessive licking in the urinary area.
Other conditions can include those such as obesity, which can cause incontinence due to weakened muscles. Kidney disorders include kidney stones, kidney infections, Addison’s and Cushing’s disease. Trauma such as injury or accident that causes damage to any part of the urinary tract or urethra.