There are several methods that are pitched to deter dogs. We have found that some of these methods are not so good. Under the right circumstances, they can even be dangerous, as they involve chemicals.

The best deterrents are an invisible fence used along with training and the motion sensor sprinkler. With the invisible fence, the dog must wear a receiver apparatus around it's neck, so it will not take care of dogs not wearing it.

A motion detector sprinkler will trigger when it detects the dog in it's range and blast the dog with a short burst of water. Works like a charm - every time!