10 Alternatives to "The Spell is Too High Level"

Options for locking off a powerful spell without tying it to character level:

1. It requires a lengthy ritual
2. It requires expenditure of gold or other resources
3. It requires certain ingredients that must be sought through adventure
4. It has a permanent cost for the character (e.g. stats, limbs, memories)
5. It has a permanent cost for the environment (e.g. sickness, drought, reality tears)
6. It requires special training from an NPC
7. It's dangerous - risk of backfiring
8. It draws the attention of powerful beings (wizards, demons, archons, etc. - arguably this is a variant of #4 and #5)
9. It can only be cast in a certain location
10. It can only be cast at a certain time (of day, month, year, century...)