There are a number of reasons why a dog may inappropriately pee in his owner's bed. Identifying the reasons for the bad behavior is the first step in eliminating it.
Dogs may pee in their owner's bed as a way of marking their territory. Some dogs will mark the perimeters of their yards, while other more timid dogs only feel secure in marking their owner's belongings, which can include the bed.
Dogs will also mark new objects to signify that it is included in their territory. If the mattress, bed frame, sheets or comforter are new, the dog may pee on them to alert any other animals in the house or neighborhood that the bed is part of his territory.
Urinary Tract Issue
A dog may pee in the owner's bed if he has a medical issue related to urinating, such as a urinary tract infection. If the dog sleeps in the owner's bed, an infection may make holding his water too difficult.
Older dogs may have difficulty getting in and out of the bed in the mornings, so they can be prone to accidents in that bed. Give older dogs their own bed on the floor to prevent this.
Dogs that mark beds as part of their established or new territory are doing so because their humans have not established leadership effectively, so the dog feels responsible for protecting the home. Keep the dog off the bed, especially at night, so he does not feel equal to you.