We planted a new tree and wanted to stabilize it with three posts, so it won't blow over in a storm, while it is still young. It turned out that planting the tree was the easy part. Hammering the 2.5 meter support posts into the ground, was a whole 'nuther problem.
One cannot use a sledge hammer on a tall post, since climbing onto a ladder and swinging a heavy weight around two meters above ground, is sure to cause a rapid, unplanned descent from the ladder.
The safe solution is a pile driver - a heavy pipe that is closed at one end.
I could not find a pile driver at the local hardware store and in any case it would cost around 65 Euro, so I took some scrap wood and a two hundred year old sledge hammer and there we go. The only expense was a handful of screws.
The thumper works remarkably well. It took longer to make the thumper than to set the three posts, but now I can also use it to drive in a sand point shallow well for the garden.
Start with a 15 cm piece of a square fence post - larger than the diameter of the stake that you want to drive in. Build a box around it such that you have a channel of at least 50 cm below the block. Strap a heavy weight above the block and there you are. It doesn't have to be ridiculously heavy.
Obviously a steel thumper will last forever, while a wooden one will eventually wear out/split, but a wooden one like this, will last long enough for use by ordinary mortals.
Do sand the wood down to avoid getting splinters in your hands while using it.
Make a mark 50 to 75 cm from the tip of the post so you can see when to stop!
Put the top of the post into the thumper, then stick the point into the ground and raise it up. Bonk the post in by raising and dropping the thumper 30 cm or so. Wedge the post with your foot to help it go vertical.Removing the thumper from the post can be tricky, since it is unbalanced with the big weight at the top, so it will likely drop onto the ground as soon as you clear the top of the post - try not to drop it on someone's foot!