Re: the cooking of rocks idea...
This should definitely work to finally get rid of all last traces of the caulerpa and you will get your rocks back (still live) in the end.

We bought our 75g from another member and the live rocks had a number of different kinds of macroalgae growing on them, some more desireable than others. We pulled off what we wanted to cultivate and threw all the rocks in a tub in the garage with powerheads on them for six weeks.

For best results, scrub the rocks once a week and rinse in saltwater. But we were lazy and just ignored ours for six weeks, stirred them around once or twice during that time, and we have nice clean rocks as a result.

This only works if there is nothing else growing on that rock that you are trying to salvage (corals, etc.)