Whether you are visiting a shelter, rescue, or breeder, you should try to find some time alone with the dog. Most shelters will have a separate room where you can interact and play with the dog. This will let you see if the dog has the appropriate temperament to be a guard dog. Qualities you are looking for in these dogs include:


High energy
Alertness
PatienceConfidence
Assertiveness
Trainability
Sociability, The best guard dog is one that acts friendly and calm when you’re not in danger but who can jump into action when an intruder or threat is near. A dog that acts out of fear and anxiety will become aggressive not just toward strangers but towards family members, children, and non-threatening guests.When meeting a potential dog, look for signs of anxiety or fear, such as:


Licking their lips
Lips pulled back
Ears pressed against their skull
Growling
Whimpering
Staring, A good guard dog will be energetic and alert. This means that they will willingly play games like fetch and tug-of-war with you. While you play with them, make sure that they are engaging with you and keeping their attention focused on you. When you are ready to end the game, they should listen to your commands to quit.Dogs that try to protect or steal toys from you may not make ideal guard dogs. Not only are they not responding to you but they may be too aggressive to be effective.
 While many people expect guard dogs to be aggressive, aggressive temperaments can make a dog a poor guard dog as the dog will attack anyone who comes near the home, not just potential threats. Instead you should try to find a dog with a responsive temperament, who will listen to commands and train easily. While visiting a potential dog, you can do a brief temperament test.


Try to put a leash on the dog. The dog should let you put a leash on and will walk next to you. If the dog snarls at you or lunges at other animals or people, they may be too aggressive.
When you play with the dog, the dog should engage and interact with you. They should not run away with the toys or snarl at you to protect the toys.
The dog should relax when you pet them. If they run away or cower, they may be too shy to be an effective guard dog.
Ask to see the dog separately.
Assess their fear and anxiety.
Play with them.
Perform a temperament test.
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