I guess as far as "can a small dog guard chickens," a couple of factors would be, how small a dog, and guard against what? A dachshund is going to be a poor match against bears. You have to consider the situation.
Do you want a noisy dog in the house to alert you against intruders? Then a terrier or Chiuahua will work, unless it is so noisy you end up ignoring it, or worse, getting rid of it.
If you want an outdoor dog that constantly guards the perimeter and battles all comers, some kind of sheep dog might do, but it won't be a house pet and you may have grooming issues.
It just depends on your situation. I don't think anyone has yet bred a good chicken-guarding dog. Maybe someone should!
Do you want a noisy dog in the house to alert you against intruders? Then a terrier or Chiuahua will work, unless it is so noisy you end up ignoring it, or worse, getting rid of it.
If you want an outdoor dog that constantly guards the perimeter and battles all comers, some kind of sheep dog might do, but it won't be a house pet and you may have grooming issues.
It just depends on your situation. I don't think anyone has yet bred a good chicken-guarding dog. Maybe someone should!