Arduino forum member 'teckel' has a few dogs at home, however they have a habit of doing their "business" indoors instead of out. In an attempt to combat this behaviour, teckel has used an Arduino-controlled ultrasonic distance sensor to detect their presence in the area that will sound a piezo siren when the dogs enter the forbidden zone. It's an interesting ... solution to the problem, or at least a blueprint for a new type of distance alarm.
If you're interested in working with piezos for various reasons we have a neat littleSOUND: sound and buzzer module:
It can be used as a noise-maker driven by your microcontroller for audible feedback of events, and it can also be used as a knock-detector input to sense events and react to them. Includes a built-in 1M resistor to allow the piezo element to detect shocks. For more information and to order, please visit the product page here.