Spot The Robot Dog is a four-legged electrically powered and hydraulically actuated robot designed by Boston Dynamics for indoor and outdoor use. Spot weighs about 160 lbs so he would be a rather large dog but isn’t that large for a robot dog. Spot would make a good guard dog as he gets around pretty well and can take a kick and keep on running. If a robot dog just isn’t big enough for you then you might consider getting a mechanical mule like this USMC Robot Mule.