ethical dilema

While I was walking my dog today another dog got under his owner's fence paralleling the sidewalk and attacked my dog. The owner has already paid the vet bill for fortunately non-life-threatening injuries though one bite could have been fatal if it went deeper. My problem is that this is the second time that I know of that this dog has gotten lose and attacked another dog. I feel like I should file a complaint to prevent more attacks but at the same time I hate to risk a dog being put down. Contradictory, since I had my pocket knife out ready to kill him when the owner's son in law pulled him away. The owner has promised to upgrade the fence.