When a male dog has an increase in frequency in urination it could be as a result of an enlarged prostate, bladder stones, increase water consumption secondary to kidney or liver disease, hormonal disorders (diabetes, cushing's), infections and even cancer.
As you can see there are many conditions that can cause a dog to urinate more frequently. If this was my patient in the clinic the plan would be:
1- Physical exam with a prostate exam.
2- CBC, urinalysis and chemistry: This will tell me the overall status of the liver, kidney, infections, sugar (diabetes), etc.
3- Based on the above findings we may proceed with xrays.
Once I have the results on the above, I will be able to explain and treat why your dog is urinating so frequently. I would recommend you follow up with your family veterinarian for a hands on exam.
Hope this helps, if you have additional questions I will be glad to answer them.