How safe is back dimple piercing?

Microdermals are pretty safe. Never ever use a bar or even a surface bar for a surface piercing. Back dimples are EXTREMELY hard to keep. Theres a ton of movement and contact in that area. You'd have to put less pressure on your back when you sit, be careful while you get dressed, and not move a lot. Which is pretty tough. Back dimple and hip piercings are notorious for rejecting within a year. I would look into getting a dermal in a better place but hey, if you really want it I can't stop you.