I've finally figured out how to get universal immunity for Life School. It'll probably work for other schools if you can find an alternative to the Amulet. The hardest thing to get on here is the spell-proof opal. You can only get it from the Star Jewel Plant which is only available from Farley's Gardening Pack. It took me maybe 3 weeks to get it from normal harvest. The pet might be a little hard, but spell-proof and spell-defy is pretty common among hatchers these days.
Hat: Jade Hood of Mystery Level 110+ (22%) Robe: Jade Robe of Mystery Level 110+ (23%) Boots: Rockstar Kicks Tier 5 (18%) Athame: Heartsteel (5%) Amulet: Rasputin's Charm of Exertion (6%) Ring: Hathi's Victory Band (1%) Pet: Any Pet that has both (10%) Spell-Proof and (5%) Spell-Defy Pet Jewel: Spell-Proof Opal (10%)