There's a cleaner you can get that will truly get the urine out. Even if you cleaned the mattress off, there is a chance you didn't actually get all of the urine trace out of it. As long as it's there, it's marked as a potty for your furbaby.
We use a line called Nature's Miracle and I buy it fairly priced on Amazon.com usually. I have one for furniture or carpet and one that's specialized to be safe on hardwood floors. It uses enzymes to break down the urine. It has a clean and light scent, not overpowering and is very safe to use.
There is also a product that is one of those "As Seen On TV" things called Urine Gone but I can't attest to it's quality as I've never used it. It supposedly comes with a blacklight that will help you see where urine is.
I hope you can find one of these cleaners or something like it so that your precious pup won't keep going back to that same spot!
