I know that at least one item (Shroud of the Battle Saint) will make a unit 'blessed' but how do you make thr leader 'sacred'? (I want to put said leader in combat with the Ark. and not go blind ... or is blessed good enough protection against the Ark?)
Given that sacred units "lose" sacred (since they get the bless icon instead of the sacred one in their attributes) when they're blessed I believe you should be fine. Run a test game if you want to know for sure.
It's too bad, whenever you build a new Temple, that you can't attach one of your commanders to that Temple as it's leader, and maybe give them Holy (+1) for as long as that Temple stands.
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You've sailed off the edge of the map--here there be badgers!