I've got 2 words for you if you have the money: ARTIFICIAL TURF!!
We tried everything--tomato juice, the pills etc. What finally worked was training them to go in an area with pea gravel. We dug out about 4 inches and put down gravel, then packed sand then pea gravel. It took them about a week of walking them to the area and training them to do their business there. There's no smell in a 5x5' area where two dogs pee.
The rest of the lawn was destroyed by their traffic patterns, so we scraped up the money (at $10/sq ft) to put in the artificial turf. It was so worth it, no muddy paws and you just hose it off. Looks real too. And they LOVE it. As long as your dogs don't dig--it's ideal.