Welcome to TU!!
Not sure what is the strongest clearcoat out there is, but I use Devcon 2ton, Etex and just started using Dupont automotive clearcoat a few months ago. All three work great but have different applying to each. Devcon and etex both have to be placed on a drying wheel after applying, so the clear dries evenly. The automotive you can spray and hang up, but have to take extreme measures to spray. You can use the search feature and find a ton of info on clears.
Patrick