Oh my god! I don't think I'll ever be able to sleep again at anchor after reading some of the opinions on this thread. I can see it now, 15 ft depth (bottom to roller) with 105 ft of rode out there on a flat night. I'm having nightmares already. Thanks for some of the good advice here, hopefully some of it will be practiced.
The "book" says optimal holding power is achieved at 7:1, now throw away the book. If you have an undersized anchor and light rode, no amount of rode will hold you. You'll see these guys backing down all over the anchorage and not setting their hook using ground tackle that's too light. Always trouble when the night winds pick up. The more iron you can put down, in lbs, the better off you'll be. There's a lot of good anchors out there, none will work if they're not the right size + for the boat.
What's the right anchor and rode? Simple, the right ground tackle it that which will hold you in place in all conditions possible within the cruising ground without causing potential harm (or anxiety) to the occupants of the anchoring boat or others within the anchorage, have back-ups, and know by practice what will work. To use a "book" formula for anchor and rode and setting procedures without practice is disaster.
Anchor, chain, nylon rode, come in different sizes and weights, and different combinations will produce different results. If you don't have the right tackle for the anchorage - don't go there til you do.