Phantom Watchdog

Conjuration (Creation)
Level: Mage 5; Components: V, S, M; Casting Time: Attack action; Range: Close (25 ft. + 5 ft./2 levels); Effect: Phantom watchdog; Duration: 1 hour/caster level or until discharged, then 1 round/caster level; Saving Throw: None; Spell Resistance: No
The caster conjures up a spectral watchdog that is invisible to everyone but the caster. It then guards the area where it was conjured. The phantom watchdog immediately starts barking loudly if any Small or larger creature approaches within 30 feet of it. (Those already within 30 feet of the hound when it is conjured may move about in the area, but if they leave and return, they activate the barking.) The hound sees invisible creatures but does not perceive illusions. It is stationary.
If an intruder approaches to within 5 feet of the watchdog, the dog stops barking and delivers a vicious bite (+10 bonus on its attack roll, 2d6+3 points of piercing damage) once per round. The dog also gets the bonuses appropriate to an invisible creature. (For most defenders, the invisible creature gets a +2 bonus on attack rolls and the defender loses any Dexterity bonus to Defense.) The dog is considered to have readied an action to bite an intruder, so it delivers its first bite on the in-truder's turn. Its bite is the equivalent of a +3 weapon for purposes of damage reduction. The hound cannot be attacked, but it can be dispelled.
The spell lasts for 1 hour per caster level, but once the hound begins barking, it lasts for only 1 round per caster level. If the caster is ever more than 100 feet distant from the watchdog, the spell ends.
Material Component: Purchase DC 3 for the lot.