Put the Beast Down

 is a quest in the Fallout: New Vegas add-on Dead Money.

Quick walkthrough

 * Gain access to the casino electrical closet and restore power to the rest of the Sierra Madre.
 * Retrieve the emergency door key to the Cantina Madrid kitchen.
 * Access the Cantina Madrid kitchen via the emergency door in the casino.
 * Confront Dog/God and convince him to back down - one way or another.

Detailed walkthrough
Before you attempt this quest, you have to turn on the power to the casino. Head straight ahead to the casino from the lobby. There will be a security terminal on your right and a hologram standing right in front of you. Change his patrol route, then head up the stairs where he was standing. Pick up the Casino Security Password on the counter next to three Sierra Madre chips. There is a speaker behind the counter above a fridge, so shoot it. A vending machine code for wine can be found on a shelf near the fridge. You want to head down the right hand side corridor, however there are a few rooms worth exploring straight ahead, one of the rooms has a terminal for the history challenge. In the room to the right of the room with the history teriminal, there is a radio. It is to the left of the autodoc ontop of a tool cabinet. In any case, head down the corridor and next to the hologram (if there is one) is a terminal that opens the electrical closet. A few steps after the terminal is the hologram projector, up on a wall to the right, at the start of the corridor behind where the hologram stands. Head back to the bar area and jump off to your left. If you look right and up a bit, you can see another hologram projector on top of a beam connected to the bar. The electrical closet is right at the back of this bottom floor area, guarded by a hologram whose projector is right behind where he stands. In the electrical closet, flick the switch on the right hand wall to give power back to the casino.

Head out of the closet, go back to the first area of the casino (where you woke up), and enter the Cantina. Disable the speaker on the top left wall. The marker points to an Emergency Key sitting on a clipboard to the right as you enter, so pick it up. You can hear Dog/God arguing with each other. Head back into the casino.

Head upstairs again, behind the counter and use the key to open the door to the Cantina Madrid kitchen. You are given the task to shut off three gas valves. As you enter, the first gas valve is on the right hand wall pretty much straight in front of you. Head into the door on your left and the second valve is on the right hand wall with all the cabinets. The third is at the back of the room, in between two doors and near Dog's walking route, so make sure you aren't seen. The second option is to talk to Dog; if you are spotted by Dog then he will set off the gas, killing you both. If you get the chance, sneak up on him and stand up to talk. If you pass a Speech check of 50, you can tell Dog to remove his collar. Since this kills him, you need to get out before yours goes off as well (which is the same result as turning off the valves). If you pass a second check at 75, this allows you to subdue Dog, which kills his character but leaves God alive. Passing a third Speech check at 85 allows you to merge both of them together. There are of course other options, such as killing God and leaving Dog, or simply killing them both in a battle.

If Dog dies either by battle or by jerking his chain make sure you loot his body. He has the Maintenance Pass that will allow you to open the sealed doors.

Any option completes the quest, but you still need to turn off all three valves before you can leave.

Note: it has a dramatic change to dogs/gods ending if you merge them together and they will not remember you but mention a sense of gratitude and will not cause him to attack you. He might confront you when you note the kitchen making this quest a lot easier.

Bugs

 * Sometimes, you are not given the appropriate option depending on who you supported at the Police Station, rendering it impossible to, for example, suppress the Dog persona in favor of God.
 * If the key/note is not read in the Pip-boy before "opening" the security terminal, the option for opening the electrical closet door will not appear.
 * If you enter the kitchen while your collar is beeping, it will continuously beep throughout that room and there is no way to stop it without reloading a previous save file from outside the kitchen. Toggling god mode on (command tgm) before your collar explodes. Also use the command tai, to stop AI function. Talk to Dog/God, get through the conversation, turn off both gas valves, and the use the 'unlock' command after click on the exit door. Not the easiest solution, but it works.
 * Under some as of yet unknown reasons, the emergency door to Cantina Madrid that is supposed to lead you to the kitchen, takes you back to the room where the emergency door key was in, giving no way to enter the kitchen and completing the quest. This can be solved by starting and completing some other quest about dealing with the team members instead, then returning to the casino to enter the kitchen of Cantina Madrid.