This is the most critical stage of life for your puppy in preparing it for work as a protection canine. This is because between the ages of 8 to 12 weeks a puppy enters what is known as the "fear stage."
What does this mean?
A fear period is therefore a stage during which the puppy or dog may be more apt to perceive certain stimuli threatening." - Meghan E. Herron
A protection service dog must protect out of confidence and NOT fear. A dog that protects out of fear does not think rationally and will not respond very well to commands.
To prevent this, your puppy must be exposed to as many things as possible during its fear stage. Caution is to be taken so that their experiences are positive ones. You're basically teaching your puppy that it has no reason to be afraid of anything.
Take it to meet new people, children, babies, cats, other dogs loud noises. The works. The more positive experiences the puppy has with the oustide world, the more confident that puppy will be as an adult.
*Refer to the pdf in the resource section to learn more about a dog's fear stage.