To my knowledge, the dispel check is ruled by two things: your caster level, which is theoretically evergrowing, and small bonuses coming from feats, prestige classes and several other sources, which are finite (as many as have been printed).
Luckily, spells that dispel other spells have a cap to the CL, so it looks like it would be possible to find the highest dispel check ever rollable. My aim is to find which caster level is just high enough to be safe (even if the dispeller rolls a 20 on their check.)
I will now show my research:
- The aforementioned cap is 25 for most spells (wall of dispel, chain dispel and that dispel that moves the spells onto your allies if you so choose).
- There is a feat that raises the caps of your spells by 2.
- The Inquisitor PrC has a +4 bonus to dispel checks.
- The Master of Manyfold Veils PrC has a +4 bonus to dispel checks.
This would mean a max result of 55 (when rolling a 20), i.e. I need CL 56 at least to resist it.
What is the highest dispel check one can hope to roll? Or, in other words... What is the minimum EL I would need if I didn't want to risk dispelling?
It is ok if a single character needs to have more than 20 character levels to get all the bonuses, but the characters should be valid and should not be using recursive cheese like the tricks needed to pull off Pun-Pun or Omnimancer builds.
Of course I'm not interested in spells that automatically dispel without checks, nor I want to go into epic spells.