ToME WikiRavenRed: Just a minor idea that this could become a non-guaranteed effect. INstead it could have an effect of Spell Level + 50 %. This makes repeated castings occasionally necesary, which might be interesting if you're fleeing the Horde of Orcs (tm)...
Edit: Oh, I should have added that I was thinking this should be trap-level dependent, rather than just being "another fail rate". In other words, it should be "(Spell Level - (Dungeon Level/2)) +50%" traps...