From page 198 of the Deathwatch Core Rulebook, available at Rank 5 for 2000 exp.
Fury of the Wolf Spirits
Action: Full
Opposed: No
Range: 5 metre radius x PR
Sustained: Yes
Description: The Rune Priest summons up the spirits of the Thunderwolves, Freki the Fierce and Geri the Cunning, unleashing them upon his foes. As long as this power is sustained, the Rune Priest is flanked by two spectral wolves that he may direct against his foes with a verbal command. The wolves cannot
be damaged by attacks nor can they be grappled (though effects that end or disrupt the power will affect them as normal). They also cannot stray outside the range of the power. Each Round on the Librarian’s Initiative, each wolf may make a single melee attack against any target within range (they move automatically into contact with their foe and are not impeded by any kind of terrain). Each attack will automatically hit unless Dodged or Parried. Freki’s bite inflicts 1d10 x PR Rending damage, while Geri’s Bite inflicts 1d5 x PR Rending damage with a Penetration of 3 x PR. Any target that takes damage from either Freki or Geri must make a roll on the Shock Table (unless the target is immune to Fear) adding the damage taken to the result.
So my Rank 6 Space Wolf Librarian (Rune-Priest, technically), gets two wolves that are immune to normal forms of damage, automatically hit for generous damage (typically sustained with a PR of 9 from Pushing) unless Dodged or Parried, and he still gets a Half Action to Smite or make an attack with his Force Axe, every turn.
So my question for these forums - what steps can I take to disrupt or end this Psychic Power? The only specific instance I can think of is using another psyker with a Psychic Hood to stop the original summons - and my Librarian often 'buffs' himself and allies before battle by casting multiple sustainable Psychic Powers, so there's no chance of an enemy psyker disrupting the ability when it happens. The trouble is, that's a smart tactic, and I don't want to punish my players for being smart. So what alternatives are there to Psychic Hoods, in this case? The wolves were a big chunk of exp for him, and he really likes them, so I don't want to take them away or nerf them into oblivion, but at the same time I need to make sure there's an element of balance in my game.