What do you use to anchor yourself ahead of a rappel / Rappel device extension?

Saw this video, and got scared a bit :)
https://dmmwales.com/Knowledge/June-...a%c2%ae-Slings

I was wondering what people use for:

1. Anchoring yourself for safety prior to rappel (I use various items... nylon sling / dyneema sling / Metolius PAS 22 Personal Anchor System - all girth hitced to my harness belay/rappel loop and carabiner on the other side to connect to the anchor point)
2. Rappel device extension, if using one (I use a 6" Black diamond dogbone connected with a rapid link to my harness)

Cheers