I got the rocks last night...it's somewhat of a success. Pricing was the best part, really. It was only $1 for a bag of natural river stones. There were also glass floral rocks (like the little balls for the fishtank, flat marbles) that I thought might look pretty, but I turned them down in favor of just starting small. The rocks are great because they are real, they are easy, a good size (no fear of them eating them) and can be reused. That meant a $1 investment for me once instead of $10.99 for carefresh every month. (I also used aspen between the rocks, but there I had already gotten a huge bag of it for less than $5. I haven't even made a dent in it and it's been a week and a half). The only downside to the river rocks is that they're a little dirty when you get them. Just like I freeze my aspen chips, I also decided I needed to clean the rocks. It was pretty easy.
Here's how I prepared them:
Soaked them in vinegar and water when I brought them home from the store. They were so icky! But, after about five minutes of soaking and rinsing, most of the residue was gone and I boiled a kettle of water and poured it over the rocks. I let them cool for a couple of minutes (I was tempted to use them for a hot rock back massage, because they felt so good on my sore hands)! Took them upstairs, where I'm putting together their new CN and filled the empty litter box with a small amount of aspen. Then, I took the rocks (now cool) and assembled them all over the box evenly, like a sort of cobblestone slab in the corner of the cage.
The girls loved it! I also introduced them to the CN for the first time yesterday so they were very excited. Daisy walked all over it and immediately started nesting with the rocks. They've sort of lost interest in it now, but I'm still hoping this helps. I just can't get them to poop exclusively in it. I never have! I put it on the opposite side of the cage, because it always seemed like there was a pile of turd adjacent to the litter box. Well, now they've put the turd pile adjacent to the now adjacent litter box. I will outsmart you, little rats! However, they have peed less on the liner, so I assume they're peeing on the rocks : ) That's a plus. It also looks prettier than litter and was great enrichment for them in the beginning. I would recommend it to using conventional litter. I think that the rocks in the aspen encourage them to do their "do" there instead of use it as a digging box.
I will be posting pictures soon!
I don't find poop to smell all that much and I even considered replacing the litter with those glass pebbles that you can get to decorate bowls with to add some nice color. My tray has a grate on it anyway so they couldn't get at them.. Just be creative and see what works out. 
