Next, take some string and tie it around the stake (ensuring the string can move freely around in a circle), measure it out half the diameter you want the pit to be and wrap that end around the nozzle of spray paint. Using the string and spray paint, mark a perfect circle, at this point you can still decide if it's going to be too big or too small for your needs or wants. Now you will need to figure out how thick the walls will be according what materials you decided on. For my application that was 10-inches, the landscape blocks were 8-inches in depth, I wanted about 2-inches for the crushed stone, and the ring doesn't really count for much, but its ¼-inch thick. Now using the string and spray paint measure out that distance past the inside circle.
Using a flat shovel make a cut along both circles, you don't need to go very deep here, just enough to scrape out 1-2 inches of soil from the ring. This will be the foundation for the walls so make it as level as you can. NOTE: Before digging, it's always a good idea to call your utility companies, or dial 811in most areas to check the location of buried utility lines. Now you will want to dig a center hole for drainage and cleaning purposes, the deeper the better, I dug mine down to 1 ½-foot. Once the hole is dug you need to take the river pebbles (or stone of your choice) and use that to fill the hole. This will allow the pit to remain drained, and even more important it will keep it cleaned out every time it rains. The stone will act as a filter, just like the gravel in a fish tank.
Because landscaping blocks usually have a small lip on the rear bottom of each one so they lock together better, you will need to break that off so they can all sit flat, level, and flush on each other. Take a concrete chisel and place the sharp edge against the lip, tap the chisel with a hammer and it should come off pretty easy. Don't worry if it's not pretty, you just need to ensure it's off so they can sit on top of each other nicely.