Step 1: Start Collecting CDs!
Step 2: Measure the Border Area
In my first project, I doubled up the CDs so the 'play' reflective side was facing out on both sides (the writing or covers faced inward). But, I found this largely unnecessary. I thought the border would be stronger with pairs of CDs but it really doesn't make that much of a difference.
Step 3: Dig a Trench
Step 4: Insert CDs!
Now place the CDs with the "play" side facing the outside. In my case, I wanted the prettier side to face the street. If you want both sides to look pretty, then double up your cds so the play sides both face out.
In some cases, I let the CDs overlap to add to the support, so you may have to have a few extra CDs to allow for that overlap. If you have the trench prepared, you should have no need to do anything other than wiggle the CDs into place. If you need to tap the CDs in to make them snugger, then lay a towel over the CD edge and gently use a rubber mallet. I don't recommend banging them bc they do break.
Step 5: BONUS
Also, I just created a border along my driveway and, at night, the CDs reflect the headlights so it looks like we have our own little landing strip.