I'm trying to come up with a way for a greedy NPC Wizard who sells spell scrolls exclusively to be used as consumables to prevent the buyers from copying the spell into their own spellbooks.
For background, the NPC has invented a breakthrough spell and is willing to share it with the world — as long as the ones who use the spell pay him each time they cast it. He spares no expense to protect his intellectual property from being stolen and will simply add the cost of the copy protection to his scroll's selling price, with him having monopoly.
What spell or chain of spells can he use to protect his spell scrolls from being copied?
I know I can simply invent an undefined spell that makes the scroll unreadable if the user tries to copy it but would prefer to go about this process within the bounds of 5th edition's current spell list. Meaning, no homebrew spells.
- Class requirement — I'd prefer the Wizard to be able to do it himself but would be open to spells in the Cleric list, and then to a lesser extent, other spellcasting classes.
- Level requirement — the lower the better, but there are no limits.
- Material Components — Free > re-usable component > consumed on cast
What I have thought of so far
Geas — the Wizard can cast Geas on each buyer to prevent him from copying the spell to a spellbook. A drawback is the high spell requirement: 5th-level, not to mention Geas can be circumvented if the target succeeds on the Saving Throw or simply waits for the Geas spell to wear out before copying it. Even with a 9th-level Geas the copier could also survive the Geas effects if broken.
Glyph of Warding - Explosive — the drawback is that the spell scroll can't be taken more than 10 feet away from where Glyph of Warding was cast. The item must be salable, which means the buyer should be able to take it home.