They only come out when the Security Level is at 2+ stars, and more will be deployed at 4 stars.
Guard dogs behave differently than most characters. You can only raise their opinion by feeding them. Having the Kennels job and raising the dogs' opinion of you makes the dogs not check you for contraband.
The only way to hide stolen keys from the guard dogs is to use the grappling hook to reach a roof of a building and drop the key over there, as long as there are no vents leading up to that roof.
Dogs are very fast, and if one is chasing you it will be nearly impossible to escape them.
They can enter the vent system (even if covered) and traverse it. They can also attack inmates who are hiding in lockers, should those inmates be a target (during Lockdown). Oddly, dogs can even enter sealed tunnels (when the hole has been repaired by 20% with soil) to knock out targeted inmates. This may be an oversight - when the medic arrives to take the inmate to Solitary, they will enter the tunnel unimpeded, only to get stuck inside once they pick up the inmate.
Dogs will find stolen keys and Keycards at all costs. If it is hidden in any container (even the Hidden Compartment of your desk), they will sniff it out and find it. If it is on a person, they will knock out the person and take the key (the inmate will then be sent to Solitary, as Lockdown ensues whenever a key is found missing.) If it is on the ground (even in the vents) they will get to it and retrieve it. If a dog finds a key in a Hidden Compartment, all other items in the Hidden Compartment are still safe.
Dogs cannot be attacked or gotten rid of in any way. Raising their opinion will prevent them from checking you from contraband, but that's the most you can do.
Dogs' behavior depends on the security level of the prison.
- At 1 or fewer stars, they will stay in their kennels.
- At 2-4.5 stars, they will choose a guard to follow around the prison.
- At 5 stars (lockdown) they will roam the prison on their own, and attack you if you have 80%+ heat.