Why would an old dog urinate in the beds?

There are a variety of reasons a dog may start urinating more frequently. In intact male dogs, there could be prostate hyperplasia or prostate cancer. In female dogs, urinary tract infections are not uncommon. Diabetes is a relatively common problem in dogs, particularly dogs that are overweight. Other causes may include behavioral changes (such as anxiety or stress), kidney failure, bladder cancer or urinary stones.

As there are numerous potential causes, some of which are serious medical conditions requiring treatment, you should take your dog to a veterinarian for an examination.