Now before I go into mym variant untouchable rules I will note that my psycher player currently hates my DM guts cos of it.
lol
So I read the Eisenhorn Omnibus and was facinated with how the untouchables were used in the game, eisenhorn used them basically as an "I WIN" button against psykers.
But when I looked at the rules in the IH or was it the other herertic one..., anyway I found them to not match my expectations.
So I combined an modified the rules for them to better fit my ideal Z( and I made the sniper assasin in the party Untouchable)
For a 3m radius around the individual: No psychic phenomenom or daemon may manisfest, No psychic power can be cast or sustained or enter ( note this still allows fireball and teleketic boulders etc). while the individuals cannot be detected within the 3m radius, this effect may also not be detected normally by a psychic power. ( I'm sure im missing some stuff aswell but what do you guys think?)
Also I will allow some particuarly powerful psychic or warp events to harm the untouchable ( but this would be a rare thing and most certainly not the domain of any creature currently with a stat line in the DH books)