Oooh, I love that! What did you put in the bottom of the ring? That seems like a great project for my boys.
ETA: They they sell the blocks in a kit so you know how many to get? Seems like that would be smart. We don't have a Lowe's here but we do have Home Depot.
ETA again: Just read an article about how to build them on the HD website. I see the liners you put inside. They sell kits but they are way more expensive than the deal you got!