The spell (http://paizo.com/pathfinderRPG/prd/coreRulebook/spells/mageSFaithfulHound. html) initially states that the dog doesn't move
It then guards the area where it was conjured (it does not move).
However, I'm wondering whether it can move once alerted? If the intruders manage to get past or run away, can it pursue?
I've always thought it was fixed to a location, like a dog on a chain so to speak. ;)
It can move about in it's area. If the intruder got past it, it would bark loudly for 1 round per caster level and then vanish. I believe the nature of the spell was to make a trap and a sentry in one, so the limitations on movement were added to prevent you from simply conjuring an entourage of invisible bodyguards wherever you went.