Okay, I'm hating it. I followed all the instructions given from multiple videos and websites and every kind of glue i used, including liquid nails, plain jane silicon, and Elmers has eaten through the foam instead of adhering it, when I tried the cement it made the front too heavy to stand. Finally decided to just put the pieces together like bricks with mortar. That works and it's getting the job done and much quicker. I just don't like the look or how much space it'll take up.
My next idea is the same concept except I was thinking three naturalish looking pillars (won't have to remove the rim!) done up with plenty of caves and voids. I'm going now to look at craft foam instead of the crud I used today, and to pick up more cement. FYI, if you do go the rock wall route, it'll take WAY more than 10 pounds, think more like 50.