Sooner or later, you will find a place where you need a small diameter, but deep hole. It'll be a mail box, a deck post, a handrail post, some fence posts, You get the idea. Some sort of post hole digger is a necessary part of a household with any yard at all. Most hardware stores have the old two handle back breakers. They look like two long handled spade shovels bolted together at the knees. They're usually heavy and they rarely ever get an enthusiastic volunteer to use them.
Good post hole digger at Lowe's
I like them heavy. When I'm givin'-it-what-for and sweating up a storm, I like the way a heavy set of post hole diggers thump in the bottom of the hole and sink into the dirt. I get a good bite, and with a little rocking, it comes loose and I pull her out and get another one. By "heavy", I mean a good strong shovel mechanism with hardwood or fiberglass handles. The light duty diggers are fine when you're lucky enough to get on a property while the fill dirt is still loose. I have actually seen cheap, light-weight diggers bend in firm settled dirt. Be prepared to pay a little more for good quality diggers and you will be much happier. Please wear boots made of leather or some other stiff and sturdy material. These diggers can really mess up an unprotected foot. They can also be pretty unforgiving on an unprotected shin. Gloves are good for preventing blisters on the hands. Cheap gloves are better than no gloves.
Then there are those times when you need a buncha' holes, or one really deep hole. This is a good time to go to your Rental Center and rent one of these;
Gasoline powered post hole digger.
This one is available for sale at Lowe's. These are great for fences, large decks and post framed buildings. They have 4 cycle engines, so there's no oil to mix. I have set so many temporary electrical services with these that I lost count. You center the hole with the point on the end of the auger, start the engine and give it gas, slowly at first. Once you get used to it, you can get a rythm to letting it dig and pulling it up to clear the auger of loose dirt. There are different sized augers available from 6" to 10". For any hole larger than 8" I'd recommend finding help and going to the rental center. You can rent a 2-man digger with the auger by the hour or the day. They are MUCH more powerful than the Lowe's Earthquake model. If the digger is a 2-man model, then 2 people need to operate it. Especially with 10" and larger augers. Please, if you use one of these, DO NOT wear loose clothing or unzipped jackets. A tie, a baggy sleeve or baggy pants can be caught by the auger and can give you a real beating before you can stop the machine.
Here in Kentucky, there are farms all over the place and fences as far as you can see. Near Lexington there are horse farms and white rail fences for miles on end. If you ever need to run that much fencing, get a tractor mounted post hole digger. Or pay someone who has one to do your fences. They can drive the line and drop a hole as they go. The attachment connects to the back of the tractor and is driven by the tractor's engine. I have seen the results of horrible accidents with these and I recommend professionals to use these.
Tractor mounted post hole digger at Tractor Supply Company.
With all of the diggers I have discussed, use caution and good sense. Plan ahead and know where you are going to be standing when you dig and where you will go if it all goes wrong. EQUALLY as important, call your local utilities and get your property marked before you dig. Nothing kills a project budget like cutting a buried phone line or a natural gas line. Most people do not have the equipment to repair these lines and it's actually better to have the utilities come and do the repairs anyway. If the repair goes wrong, and they did it, they have to fix it.
Tom in KY, call before you dig, use your head, then you can hurt your back.