I suppose that's something to think about. You would have to explore your local laws. I imagine it would be up to them to prove in court that you're taking rock from the ocean, and I would think good records and receipts tracking your dead rock purchases would go a long way towards making that hard for them. That said, it's easy and cheap to register and LLC and as long you're charging and paying sales tax your business records should do the trick.I’m not versed in these types of laws but I’m pretty sure the rock idea you have to have a lease and/or aqua culture license or similar otherwise if your stopped by FWC how are they to know where the rock came from or if it’s legal/illegal.
But I'm not a lawyer so if I were going to do this I would consult one for advice first.