Often these areas are not in the city, and in areas where it is not illegal to allow your dog to be unleashed.
But the owner is liable for damages to your property ( your dog is considered property) Also there can be criminal charges for damage to your property if they show a careless attitude to control their dogs action even if no leash law.
Also a person has the right to protect their self ( not their property) by use of force. So if I walked out into my yard, and a dangerous dog was in my yard and that dog had previously had a record of attacking animals, and it growled at me,
Well lets say that the dog would never walk off my property. I would protect myself.
A fence of course to keep your dog in, and their dog out would be the best answer