Bladder disease can cause urinary incontinence or an urge to urinate frequently.
Cystitis is far more common in female dogs than in males. If your dog has cystitis often the first sign you will notice is that it is passing small amounts of urine very often. Sometimes you will see blood in the urine and occasionally your dog will strain as if trying to go to the toilet but nothing comes out. In these cases cystitis may be mistaken for constipation. A few dogs with cystitis become very thirsty and some dogs feel a bit 'off colour'.
Urinary incontinence means the loss of ability to control urination and can be caused by a variety of diseases. Incontinence is quite common in dogs but is usually more of a nuisance to the owners than a cause of distress to their pet. Urinary incontinence is more common in females than males because of the anatomical differences in the urinary tract especially the shorter urethra in the female. It is rarely seen in cats. If your dog is incontinent you may see urine dripping from its vulva or penis or, more likely, you will find wet patches where your dog has been lying. Sometimes there are only tiny wet patches or the bed may be soaked. Often the urine is quite dilute and might not smell very strongly.
If you think there may be something wrong with your dog's toileting habits then you should make an appointment to see your vet. Try to collect a fresh urine sample and take this with you when you take your dog to the vet. Your vet will be able to get a lot of information on what may be wrong with your pet from testing the urine sample.