How deep and wide depends on where you live. If you have wet/freezing temps consistenet in the winter, you want to go below the frostline in your area. You can get that info from your building dept. If freezing isn't a problem in your area, you have to consider the soils type. If it's loose, then you are going to want to go wider but not necessarily deep. Making the hole wider at the bottom and narrower at the top helps to keep from rocking. Too loose of soil you can go wide and fill with compactible filler soil and tamp the bottom and sides. In real rocky soil, non freezing, you can typically get away with minimum width and depth but in all cases, dig it out deep enough and wide enough to get some gravel in the bottom as well as around the sides after setting the post before concrete for drainage as mentioned above.

I think you will say its awesome.. :-) I have to go down 42" to get below the frost line here in northern illinois.. the concrete would be poured around the sleeve first.. so once that sets up you can drop the post into the sleeve.. really I could fill have the sleeve with gravel after that point.. as the post only goes down that far to deal with the frost line.. so I could drop another 10in of gravel into the sleeve and drop the post on top of that.. there would still be 32" of post in the ground.. also whats the harm it in overflowing? seems to me that would take a lot of water.. it would have to soak down to 42inches of soil then fill all the back up assuming it doesn't just keep soaking down in the soil underneath the gravel.. wouldn't all that water just get soaked up by the concrete anyway or pour in through the gap between the post and the concrete at grade.. and the concrete would hold it against the post while the sleeve allows it to drain and or/dry....with the sleeve going all the way down at least the water would have somewhere easy to drain to and the ribs allow for air/drying.. it's not my idea.. these two companies came up with it.. this is the link to the company that sells this product.. http://www.postshieldusa.com/cs/ or this other one.. http://www.postprotector.com/.. i'm just not planning to buy their sleeves but use the pvc sleeves just laying around lowes instead.. i am looking for better alternatives besides dont use ceder and dont use concrete.. seems to me that if any alternative is going to end up with rot eventually why not just make it easier to repair.. i also like the idea of the copper because I intend to use copper on the post caps.. and if it works and looks cool that would be great.. but if that just marginally improves the longevity of the post but you still end up having it rot out and need to remove the concrete then why not make that part easier.. don't know.. these companies at least have me convinced but like they say a sucker is born every minute.. so maybe im that sucker.. I'm here hoping somebody can save me from a dumb idea but it at least seems logical to me.. the post prevents post to soil and post the cement contact which from what i hear are the two things that kill the post..

Gernerally I put gravel in the bottom of the hole and about 1/3 of the way up the post. Then pour concrete up to about three or four inches from ground level and slope it away from the post. This lets you plant grass right up to the post and hide the concrete and with this method the water seems to drain away just fine, I have some posts that have been in the ground for several years and are still holding good as new. If you want concrete showing above ground then go ahead and pour a cap, no big deal. If the concrete is sloping to the posts then just dig out a little dirt and take a cold chisel and knock some of it off, new concrete should not be very hard to break off.

I had a similar problem at a house I lived at years ago. A fence contractor came out, took the caps off the affected posts and inserted metal sleeves (it took a bit of hammering with a mallet to get them all the way down). It worked really well and the fence was still going strong when I moved out several years later. I don't know if he made the sleeves custom or they are a readily available product. If you can't find them and have access to a wood lathe, you could always take a piece of 4x4 redwood and turn it to the right diameter to insert into the posts. I've done that with rusted out wrought iron fence posts and it works well (the wrought iron is easier because the posts are square so you don't need a lathe).