If you turn into a Rat using Cloak of the Sewers, you earn 90% resist to all Melee damage (piercing, blunt, slash)
Using The Tob ability that grants +40% resist to all melee damge gets you up to 127% resist in every Melee damage (Immune to physical attacks)
Add to that the fact that with a high level monk you can easily have 100% magic resist, and voila : invincible Monkey !
Just, instead of doing 30-50 dmg per hit, you do 8-10 dmg
Using Greater Whirlwind with this combo shall compensate for the lack of damage per hit (doing 10 x 8 dmg per round is still nice, since you are invincible hehehe
btw: I'm soloing SoA and ToB as a Monk and i'm having a blast:
98% resist to magic, Immune to +1 weapons, -19 ac (yes.. -19 !)
and thaco of -9 (shall become -11 once i get Fire Giant strengh belt), pounding ennemies for 30-50 dmg is just.. well.. Powerfull
Edit: and of course, got all that without using a single cheat, no CLUA or anything)