Itís pretty easy to tell when a dogís nervy around strange people. Heís jumpy and on the alert: either he canít sit still and is constantly fidgeting, leaping at the smallest sound, and pacing around barking and whining; or heís very still indeed, sitting rock-steady in one place, staring hard at the object of his suspicions (a visitor, the mailman, someone approaching him on the street while heís tied up outside a store.)
Why does it happen?
Thereís one major reason why a dog doesnít like strange people: heís never had the chance to get used to them. Remember, your dog relies 100% on you to broaden his horizons for him: without being taken on lots of outings to see the world and realize for himself, through consistent and positive experiences, that the unknown doesnít necessarily equal bad news for him, how can he realistically be expected to relax in an unfamiliar situation?
What can I do about it?
The process of accustoming your dog to the world and all the strange people (and animals) that it contains is called socialization. This is an incredibly important aspect of your dogís upbringing: in fact, itís pretty hard to overemphasize just how important it is. Socializing your dog means exposing him from a young age (generally speaking, as soon as heís had his vaccinations) to a wide variety of new experiences, new people, and new animals.