[F. Gottwald]

i know that secret word (or similar) followed by breach and a tank rush works... the point i was trying to make is that there are usually more efficient ways to kill enemy mages with less of a risk for your party and less spell slots expended.
skull trap was just an example (the one that usually works best as most mages don´t resist magic damage). every wizards protections has a flaw somewhere... and if you can´t find one, getting him to expend his spells on a character or summoned creature with magic resistance (polymorph into a mustard jelly) is more effective.

if you´re going to risk your whole party in a tank rush (usually not a good idea, with breach or without), you might as well use weapons that deal non-physical damage (acid arrows, flail of the ages, crom faeyr etc) which will get through their protections anyway... if you get close enough to actually hit them, they have as good as lost anyway as you can disrupt every spell they attempt to cast.