A rock?? Isn't that a much bigger risk of accidentally crushing the quick?
You can use normal human nail clippers or buy special guillotine-style pet clippers. Either way you should be able to see the quick (red vein in the nail) and neatly cut far enough away from it. If your bun has dark nails that's much harder though. To be safe don't cut too far behind the fur line, or just cut it tiny bit by bit every week.
If you really don't feel confident enough to do it yourself, you can always take your bunny to a vet, breeder or rescue to do it for you for a small fee.