Finding shorts in PCB's can be a nightmare. Digital multimeters typically don't measure down to the <1mOhm level required to trace down where the fault is located. This "Model 1000 Short Finder" seems a bit basic and costly for what it is, but it's another worth it's weight in gold tool when it's needed.
Update – This simple but really useful multimeter add on improves on the short finder above: jaanus.tech-thing.org/category/half-ohm/
Its a simple op amp circuit which displays mOhm readings as mV on your multimeter and well worth having as part of your workbench toolbox. You can easily make it yourself but the ready built module from shop.tech-thing.org fits right into a standard multimeter such as the fluke series.