We have K-9 grass and it works like a charm. Daisy is 8 months old. We've used "potty grass" since we picked her up at 10 weeks. She immediately starting using the potty grass with no training. Some of the pre-made dog potty sites have "how to train an older dog" instructions.
We didn't buy one of the "pre-assembled dog pottys" that use K-9 grass. We bought an unbound cut of the grass (large enough for 2) from the manufacturer and then bought a "cage/crate tray" -both off the internet. We cut the grass to fit the tray. It measures about 22 x 36. I put "pee-pads" under the grass to soak up urine and it eliminates any urine smell. Poop still smells!
We pick it up with a tissue and flush it down the toilet.
We have two pieces of the grass - so I have a spare to put in the tray after I wash the dirty one and it's still drying. In th summer - we would pour some Simple Solution on the grass and hose it off - then leave it to dry in the sun. For the winter, I have a laundry sink to rinse it in - or we can hose it off in the shower. I leave it to dry down in the basement.
When Daisy was little - we placed the pan on the floor and she could easily climb up on it. When she had grown a bit, she had a problem determining if her rear end was over the grass. She'd get her front paws on - and pee on the edge of the tray.
We built a frame of 2 x 4's and put the tray up on it. She has to get up on the grass and she hasn't missed since we elevated it.
Daisy has been the easiest puppy ever to housebreak. She's been very reliable since she was about 4 months old. We have a fenced back yard - and a sunroom with a sliding door that we let her out through. We keep the potty grass in the sunroom close to the door. Daisy prefers to go out in the back yard and has a bell by the sliding door that she rings to let us know she wants out.
When we go out - we restrict Daisy to the sunroom (gate across the doorway). She will use the potty grass if she needs to go while we're gone. Every once in a while in the morning - she will ring her bell to go out - and then jump up on the potty grass to go. I think she just can't wait until I get to the door! I was hoping she would use it more in the winter - but she LOVES the snow and still only uses it in an emergency.
It gives us peace of mind to know she as an acceptable place to "go" if we're out for the evening. I don't feel guilty if we stay out longer than planned and don't have to wonder if Daisy is in misery trying to hold out!
Here is a pic of Daisy scratching at the door to get in, her "potty bell" and her K-9 grass on the 2x 4's.