I need help figuring out what to use for the seaweed that will actually last in 100+ weather thanks in advance

I think this is a duplicate post.  Someone answered suggesting the use of gp on wire that is then dipped in melted chocolate so exposed wire does not go into the cake.

The picture looks like the seaweed is made with royal icing and a leaf tip.

I agree with @Karengtr ‍ , royal icing would work (let it dry completely) or gum paste either one, as @kakeladi ‍ said (also completely dried).