Actually, I do (chemistry background). GAC will remove detergents from water - very effectively, I might add. That assumes, however, that the detergent will effectively desorb from the rock. The other possible item in the "lemon scented bleach" is limonene. This will also be effectively removed from water by GAC. One note - limonene is one consituent of of at least one popular coral dip on the market. I wouldn't want to dump it in my tank, but it appears not to be directly and immediately toxic to corals.
Given what you've noted is the history of this rock (outside around a pond for a couple of years), I'd be a lot more concerned about organic buildup from terrestrial critter waste, and I'd also be concerned about the rock's true identity as originally being actual old coral skeletons. If it is no-ifs-ands-buts-or-maybes Fiji rock from the ocean, then I would most certainly give it an acid bath followed by at least a few weeks in circulating RODI, with a complete water change every few days.
That should at least make it safe to use, though you may well have the standard problem of "the uglies" until it cures for a few months in your tank.