help! My dog refuses to be potty trained!

I would like to think that I am a very patient pet parent but it's been over a year and my dog Brownie is still not potty train! What's going on? We have tried everything under the sun. Our older dog, Pork, was first tought to use the potty pad, then cat litter (that was great), and now Wiz Dog. Brownie was eating the cat litter so we tried the Wiz Dog since it was highly recommended by some folks on dogster.com. Pork has always taken to whatever potty system. He understands that if it doesn't look like a bathroom, it's not. Brownie is inconcistent. He was making progress and using the Wiz Dog for pee and would poo around the tile areas of the house. He enjoys the grass and does his business outside when we go for walks. We have read every book and exhausted every idea we could think of. If you guys have any good ideas, please let me know! The good thing is we have one superstar...