Hi I'm Rosie one of the vets and I'd like to try and help you and Buddy. I'm sorry that you are dealing with this - it can be an extremely frustrating problem. The most obvious thing is to get a urine sample checked by your vets - I suspect you have done this a long time ago, but infections and bladder inflammation can cause problems like this which then just become habit. If you haven't, I would get him checked for infections and crystals (microscopic bladder stones). This doesn't need a whole consultation - most vets should be happy just to look at a urine sample and let you know if it's ok.
If it's ok (and I suspect it is) then it is time to look at other things. I would definitely check what you are cleaning the areas where he urinates with. Anything containing bleach or ammonia will just encourage him to go there again (he will interpret those smells as another dog urinating on his patch). You definitely have to use a biological cleaner - when I was training my dog I used a solution of biological washing powder in a squirt bottle which I found far easier than anything else. If he has been doing this for a while I would even go to the length of using a black light to check where he has been (it will glow), and clean those areas thoroughly.
Once you have done this then I would start clicker training him. You should easily be able to buy a clicker in a pet store, from your vets, or online. With the training, the clicker gives him positive reinforcement quicker than you can speak, so dogs respond to training much quicker. To use it properly, for 48hrs everything he eats needs to be given click-eat (i.e click - throw a piece of kibble - and repeat) including all his meals. This will really stick in his brain that this is a really good thing.
Then, I would take him (don't carry him, walk him) to where he wants to urinate and wait with him until he urinates. The second he urinates in the correct place, click-treat. I had to do this with my dog as he was a rescue and not trained at all, and it can be a very frustrating process as I seemed to be forever waiting for him to urinate in the right place so I could reward him. But, if you persevere it does work. It is a question of putting a lead on him and walking him to where he needs to go, waiting as long as it takes and click-treat when he does. If you carry him his brain doesn't register where he is going and it won't work. You need to be taking him every couple of hours. I would crate him overnight as dogs generally won't urinate on their beds.
The other thing to think about, if he isn't already, is castrating him. Sometimes this can have a dramatic effect on training and some dogs with this problem stop urinating in the wrong place simply by being castrated. Obviously, if you want to breed then this isn't an option. Some vets (and you'd have to check with yours) can offer a temporary chemical castration to see if it will help, if you want to trial it before the operation. We use a suprelorin implant, but again each place is different so it is worthwhile checking with yours. The implant lasts about six months then wears off.
I hope I've helped - if you have any questions from this or need clarification then just get back to me. Otherwise, if you have found this useful, please leave me a positive rating. Thank you, ***** ***** luck, Rosie.