In my opinion zoanthids are the #1 resistant to peroxide although it may irritate them for a while. Valonia sure is rough agreed, I fear importing it into my tank for sure.
The best way to treat in my opinion is to remove rocks it's on, set them on the counter, and use a knife to detail surgically dislodge and rinse away all the material rendering the rock seemingly clean (but there's still small holdfasts and plant material attached to rock usually, it's why they're a scourge) and then in the clean condition, directly apply your peroxide or vibrant from a used bottle you got off ebay right to the cleaned areas, let sit a bit, rinse and put back and cross fingers.
I didn't like dosing so many chems into the water since the stuff is so resistant, but agreed vibrant/ whatver it was / was the strongest valonia kill our hobby ever found. If vibrant was better at writing label ingredients disclosures it would still be here.
Vibrant was not killed off due to bad performance, it was killed and fined heavily for not disclosing active ingredients/ some say misleading labels. It sure helped a lot of tanks we can see in Facebook posts and forum posts when it reigned. As mentioned the crabs and certain fish might work, but nowadays there's marked disease import risk to the display if we start adding random unfallowed animals in response to a challenge. It wasn't like that fifteen years ago.
