I would employ the use of a video camera. Film the dogs on your property (that will not injure them). Use the footage as evidence. Make sure the dog's owners see the footage. I would certainly give them a chance to make what is wrong right (I, too, do not believe it is the dogs fault. It is also the neighborly thing to do). If that doesn't work, the county sheriff will certainly love the footage when "dog at large" charges are filed.