Preparing ex-live rock for new tank setup

[MarSch]

I scored a new tank and some ex-live rock from a fish store that was shutting down. It was out of the water for a few days at least.
What is the best way to prepare the rock to ensure it is thoroughly free of all unwanted stuff?

I'm not trying to rush anything, I'd prefer to take the time to get it right.

I've scrubbed it all thoroughly with a brush, rinsed it well in filtered water and now have it in a spare tank covered with salt water. No powerhead in there yet for water flow but I'll be adding one soon.
I've also covered it to block out all light. I've read that this will stop any algae thriving and let any bacteria take over.

But I've also seen threads about needing to remove the PO4, and seen suggestions like dosing with lanthanum chloride or using GFO.
Can I use Seachem PhosGuard instead? I don't see why not, but I've not seen it mentioned.

Anything else I should look out for?

 

[Super Fly]

if it was me, I'd bleach the rock to kill anything bad, rinse and start over by curing it in brute. U never know what may lurk in any used LR.

 

[MarSch]

Thanks @Super Fly , I will do that.

I've seen other posts about a 2 stage process:
1. Bleach
2. Acid

I think I will do this, but will use vinegar instead of a really strong acid.

Does it matter what order I do this in? Can I do the acid/vinegar soak first, or does that defeat the purpose somehow?