I would like to know what breeds of dogs make good guard dogs, but won't eat my chihuahua and yorkie?

I'm moving to the country and would like a guard dog for when my husband isn't at home, but I have a yorkie and a chihuahua and would ideally like the guard dog to get on well with them, so I wouldn't have to keep them separate. The guard dog would have to be suitable for both indoor and outdoor living, and not prone to straying/ animal worrying as there is a lot of livestock near where we will be living. Ideally, the dog should be easy to train. Hope someone can help. Thank you!