Over the weekend I put up a short length of wire netting fence to keep the rabbits and chickens out of our vegetable patch. A couple of the posts I knocked in weren't perfectly vertical so I damped the ground down (some more) and wedged a length of wood against them to push them straight with a metal stake at the other end to stop the length of wood slipping.
We have something like half an acre (or maybe even an acre) of grass around our house and there's just one MDPE pipe running across it. One of the two metal stakes I drove in was a perfect hit on the middle of the buried MDPE! I only found out when I pulled it out and got a pretty little fountain out of the lawn.
It wasn't too much of a disaster as there is a separate stop c*ck for all the garden water and I had a straight connector to fix it with. It still amazes me that I managed to hit that pipe though.