We had one sly fox that took us for granted and didn't live to make that mistake again.
We keep Rat Terriers, standards from 15 to 30 lbs, not the 'dust bunny' sizes and they do their job. I once had 45 goats, 47 if you count the bucks. Not once did I lose a kid or bird to the two separate packs of coyotes in our area and they were pasture born with the most at one time being 27 new kids. When the pack of coyote would sing, my pack answered challenge. They may not have known the size of the dogs, but they knew the heart of the dogs. They accept no tresspassing in their territory. All we ever did was hear them.
Producers around me lost dozens of kids, lambs, chickens, and once they pulled down a 3 month old calf on a close neighbors place.
Would I trust my Ratties in with my birds? No, their prey instinct is too strong. Do they hunt my birds? No! They have never in 7 years gone out of their way to attack, or try and get to my poultry. The chicken yard shares a wall with my largest boy's kennel and he's 36 lbs of Rat Terrier. My geese share the same yard as all the dogs in a pen of their own. My grandkids share the same yard. Before anyone starts to 'ewww' about dog 'poo', we have snakes. In that yard, we have no snakes. The dogs won't allow it. For something to get through the fence and into the chicken house it has to come through my Ratties. That doesn't happen. The yard stays clean and the kids wear shoes.
The main thing is I don't worry about snakes biting my grandbabies or anything marking my birds as an easy dinner. One mile down my road a friend killed a 3 ft cottonmouth viper on his pool deck. One that big means there are more. You can bet they'll give my yard a very wide pass distance.