How to hang load from ceiling I-beam joists behind drywall?
If you don't mind the look, I'd suggest a 2x6 run perpendicular to your joists. Ideally, you'd get 3 joists (so a 2x6 slightly longer than 4', assuming you've got 16" spacing) with at least 2 good 3.5" #10 screws each. (Since these are pretty big screws, you'll want to drill pilot and clearance holes.) To attach the rock rings, use 6/7mm -ish cord through holes you've drilled in the 2x6. (If you don't want to dent the drywall, just chisel a small channel across the top of the holes.)