I am sorry to hear of Clide's urinary troubles and I am very concerned about him based on what you have told me. There are 2 reasons that a cat will posture and try to urinate and not be able to. One is that his bladder is inflamed and he feels like he has to urinate but his bladder is empty. This can happen secondary to crystals, stress, bladder stones ornery rarely an infection. In a cat Clide's age, I am suspicious of a condition called idiopathic cystitis. Here is a link more information about the condition and what we know about it in cats http://www.marvistavet.com/feline-lower-urinary-tract-disease.pml
The other reason that cats will posture to urinate and not be able to produce urine is because they have an obstruction of the urethra and are physically unable to empty their bladder. This is a life threatening situation and can cause renal failure, electrolyte disturbances and death if left untreated. The best recommendation in this case is to anesthetize the cat and pass a urinary catheter and relieve the obstruction. Afterward, he should be hospitalized with the urinary catheter left in place and IV fluids to flush out his system. Generally the catheter is pulled after 36-48 hours (depending on the hospital, amount of urine flow, color of urine, etc) and then he is observed for spontaneous urination If he urinates on his own, he can go home for further monitoring at home. If he is unable to urinate then surgery or re-catheterization is recommended.
Because either of these conditions involve discomfort. pain medications are also given along with IV fluids and sometimes other medications and to reduce urethral spasms and help the urethra relax and possibly a special diet to change the pH or composition of the urine if indicated.
The only way to tell the difference between these two conditions or situations is to feel the bladder and if it is large and firm, he is obstructed and needs a urinary catheter to be placed. If the bladder is small then he is not currently obstructed (but may become so in the future) and he needs to be put on pain medications to help him be more comfortable until the inflammation subsides and he can urinate normally again.
Because of the life threatening nature of this condition, I recommend that Clide be taken in and evaluated by an emergency veterinarian right away. I hope you have found this helpful. If so, I would appreciate a positive rating as I am not compensated otherwise and the website will not know that I have been helpful. If you need additional information or clarification, please do not hesitate to ask. I strive for 100% customer satisfaction. Best regards,