I need to dig a hole at the front of our place to install a new letterbox (thanks to some scumbag stealing ours overnight). In the area that I live, all services are buried underground, so I'm a little apprehensive about just digging, just in case I hit one. I only need to dig about 40-50cm down, so I'm not even sure whether my concerns are justified.

The last time I had to do something like this was when I dug a trench for foundations for a garden wall I built in Australia. Over there, they had a "Dial before you dig" service, which you could ring up and get plans to show you the locations of all the services in your area. And when you were digging, you hit some yellow warning ribbon well before you hit the actual wires or pipes that may be buried down there.

What precautions do I need to take here? I tried doing a little investigation, but my Google Fu only threw up results that seemed to be more suited to contractors performing much larger excavations. The advice was along the lines of:-

1) Contact each service provider separately to get a map of their services for your area
2) Refer to the map when digging, but don't take it for gospel
3) Use specialist equipment to detect buried services, but don't take it for gospel
4) Due to the above possible inaccuracies, you may want to arrange for a company rep to be present

Is it really necessary for all this for a simple hole out the front? And are there approaches I can take to ensure I can make a reasonably accurate educated guess as to where I could dig without disturbing services?