When digging a grave by hand, haul away 17 wheelbarrow loads of dirt and pile the rest by the hole. You will have just the right amount to backfill.
When you are working in the vicinity of high voltage, keep 1 foot of distance between you and the power source for each 1,000 volts. For instance, stay 13 feet away from a 13,000 volt power source.
Wish I had a penny for every time I needed to have those rules of thumb at hand (sigh) while working the reference desk! Now that I've discovered the superb rulesofthumb.org, I'm prepared to field any question that comes my way!