Signs of urethral obstruction include attempting to urinate frequently, straining to urinate, and passing bloody urine. The disorder can be life threatening. Therapy is geared toward removing the obstruction and treating its cause. Most common urethral obstruction develops when your dog has bladder stones, and one or more of these stones lodges in the urethra. Other conditions that narrow or completely obstruct the urethra include inflammation due to bacterial infection or crystals (the building blocks of bladder stones), trauma, tumors, and diseases of the prostate gland. Sometimes urethral obstructions can be treated with medication and diet, but surgery is often times needed.