The only way to really know that is to know how many horns were decorated, and then how many had bible verses.

Rather impossible. It appears that most horns were self-made, but even that is conjecture, as one cannot tell if the horn and the engraving were done by the same hand, no? The best answer seems to be, a bible verse on a horn is not incorrect, as it was known to have been done.
You may want to find text from an old King James Bible to ensure the actual wording and spelling is correct.
For example, a modern translation of Psalm 18:2 is,
The LORD is my rock, my fortress and my deliverer;
my God is my rock, in whom I take refuge.
He is my shield and the horn of my salvation, my strongholdBut the King James version of The Bible was the most common, for protestants. The Vulgate edition was for the Catholics. The KJB version in some editions is:
The LORD is my rock, and my fortress, and my deliverer; my God, my strength, in whom I will trust; my buckler, and the horn of my salvation, and my high tower.Just a thought...
LD