Steveo
Those sorts of machines can be nasty if they hit a rock/root as others have said.
If you are looking at a hobby farm situation, then a tractor or dingo are a good machine to have, as one of the more useful things to have is a hydraulic 'bucket' for moving soil, lifting etc.
You can also fit auger for holes.
Unless you are doing lots of fencing, almost easier & cheaper to get a contractor in with hydraulic post driver (for pine posts) and you can put in the steel star posts by hand or get one of the mechanical (compressed air, electric or petrol powered) for driving them. (operate them while standing in back of ute and posts go in easy).
Not sure what you plan for with fence design, but many farm fences now use pine posts 20-30 metres (or more) apart with steel star posts as intermediates.
Also take a look at a Slammer Tool as it far beats a crowbar for ease of use -- badically it's a slide hammer powered crowbar with a diamond shaped blade. Kiwi designed
Joe