Deterrents can be almost anything in the game that creates a huge problem for your opponent so in order to make things easier I've decided to split them up into two types: Active and Passive.
Active deterrentsThese are things that require activations when your turn comes around, like Bile Thralls that can basically go "you charge my lines... dude... your army melts" or Tartarus that goes "Did you know that ganging up on my chicken puts you in perfect Thresher formation?". Active deterrents are easy to use and makes it impractical or dangerous to hit your army where it hurts.
- Bile Thralls (Purge)
- Withershadow Combine (Unbinding and Dark Industries)
- Tartarus (Death Toll)
- Machine Wraiths (Machine Meld)
Passive deterrentsThese are hilarious but often harder to use well. The passive deterrents take effect in your opponents turn and makes his choices harder, his models die, or his actions fail. The Shadowhorn Satyr is a great example of a passive deterrent since missing him with a charge attack means getting knocked down. He has set defense so an charging heavy will need to hit defense fifteen (or be immune to knockdown) on his first attack to avoid the effect.
- Defensive feats (Harbinger, Old Witch, etc.)
- Defensive spells (Admonition/Enliven, Dragon's Blood, etc.)
- Defensive abilities (Riposte, Retaliatory Strike, etc.)
- Effects that trigger on hit/damage (Protective Fit, Hyper Aggressive, etc.)
Combining deterrentsThere's nothing that prevents you from stacking active and passive deterrents and it often ends up being some incredibly powerful options. Admonition (eSkarre) will prevent your Helljack from dying when an enemy Warjack comes gunning for it. Dark Industries (The Withershadow Combine) could turn an enemy heavy Warjack into a Seether after it destroyed your Helljack.
If you combine the two your Helljack survives and you get a Seether on top, gaining a massive lead in the war of attrition. There are several combinations out there, or deterrents that can be increased in power with the application of the right spell or ability, so keep an eye out for possible synergies when constructing your next list.