Help with dog peeing on car

ok, I have a medium size dog that constantly pees on my passenger side door, front tires and front bumper. I read and tried ammonia for two months straight to keep him away. It seemed to work since he no longer peed on the car and once stopped he did not pee on the car for about 2 months.
   
Now he started up again. It looks like someone dumped a bucket of urine on my passenger door and my tire. I just do not know what to do anymore. If anyone has any ideas that would be great.
   
I read waiting for him to use the restroom and catching/correcting in the act but how am I supposed to sit and watch him 12 hours a day everyday?

First of all, clean every area he hit with pee with Nature's Miacle or the like to remove all traces of the scent.
   
The smell of his own piss is like a beacon screaming at him, 'PISS HERE FIDO, PISS HERE FIDO' that he cannot resist.
   
Second, the way you watch this dog 12 hours a day is to tether him to you. Now he can't slink off and piss the car.
   
He gets hourly potty breaks just like a little baby, praising him for a correct potty (in essense, remedial potty training). Go with him. He is not trustworthy and you have to monitor his every squirt until he's back on track.
   
If he doesn't like it, tough. He lost his freedom when he pissed the car.
   
If he even looks sideways at the car give him a sharp, "Fido, NO" and redirect him.
   
Essentially the best way to keep him from pissing all over your car is to keep him away from the car and force him to empty his bladder elsewhere.
   
This does require some effort on your part since you can't just let him out to go potty and hope he'll do right, since he has proven that he won't.
   
After awhile, when you think he's gotten the idea, let him out on his own but let him know you are watching and see what he does.
   
If that goes OK, then next time let him out but DO NOT let him know you are watching. If he starts to squirt the car, you've finally caught him in the act and now you can give him a sharp "FIDO, NO" and stop him, direct him to the spot you want him to pee in and praise him if he squirts his load there.
   
Contrary to the current crap dog 'pop psychology' dogs DO know why they are being punished even if you don't catch them in the act, so I am not opposed to showing him his mistake and telling him "NO" but if you don't want to, that's up to you.
   
If you catch him near the car, give him the sharp "NO" to remind him that he is not supposed to unload on the car.
   
Dogs do not like hearing 'no' so this will be a harmless reminder to him that something a little bad happens when he goes near the car.
   
Good luck, hope your car is soon pee-free.