String him up by his privates and yank the cord each time you find a puddle, is what I would do. Although the baseball bat has a certain appeal...

 kidding.

 I know they mean well, but people who keep saying "you have to catch him in the act," hasn't met my dog or me. I work for a living, and have to have sleep. My dog, on the other hand, sits in the dark corner of my bedroom and waits, and watches me. He waits for exactly the right moment just when I start to fall backwards into the abyss called sleep, then he lets out a large fart and relieves himself in that yellowing corner of my bedroom. I swear, that's the only time he does it: when I am out, literally and figuratively. Even if I were a stay-home person liek a retiree or something, who the hell watches their dog's every move 24/7? What, I don't have a life?

 I agree with the bat boy below, but I think that a good cleaner, one that is enzyme-based, will work well with the repellent. Otherwise, it will happen over and over again. The area should be saturated with the cleaner and allowed to sit for a while...longer for tough stains. Then apply the repellent. Incidentally, enzyme-based cleaners also act as repellents.

However, because you can't really use the repellent on your whole house (or can you) the dog should always have access to the potty area, even when people are unavailable for walks when they are at work for instance, or when they are asleep. If you want to prevent him from getting to that spot or getting into the attic where the spot is, you might also want to look into fencing the dog out with ultrasonic sound waves. It was originally invented as an invisible outdoor fence for dogs, but there is no reason why that should not work indoors. This would also eliminate the scratching on the door, which inevitably just gets on your nerves until you give-in and open the damned door. A more simpler solution is also to place a piece of large furniture or a big potted plant where the spot is, after it has been thoroughly cleaned.