Tenacious Spell (Metamagic)Source Ultimate Intrigue pg. 94
Your magic is difficult to unravel.
Benefit: Increase the DC of caster level checks to counter or dispel a tenacious spell by 2. If a tenacious spell is dispelled or dismissed, it lasts for 1d4 further rounds (to a maximum of the spell’s normal duration) before ending (this does not occur if antimagic field or a similar spell or effect suppresses or ends the spell’s effect without dispelling or dismissing it). The lingering auras of tenacious spells detectable with detect magic last for twice as long as usual after the spells end. A tenacious spell uses up a spell slot 1 level higher than the spell’s actual level.