sorry for the lack of detail!
what I ment by "cut the tarmac with a grinder" was this:
you are aiming to have a clean cut square in the tarmac with a hole in the middle for the post to be concreted into. The cleanliness of the tarmac extraction means that it is much easier to "make good" with the instant tarmac at the end and thus give you a better looking job.
the "medium grinder" was an indication that you need a cutter disc that is capable of cutting thru the tarmac depth i.e. a small disc may not be able to cut deep enough.
by "breaker" i mean the power tool used to excavate the hole (if concrete of stone is present). I`d suggest 2 levels of tool:
1) an SDS drill fitter with a pin or chisel
2) a "KANGO" style hand-held breaker gun
i.e.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 01304&rd=1
ask at any hire shop for a "Kango", they`ll know what you mean.
HOLE SPEC:
*****************
usually for a good quality job you should always concrete the post into the ground AT LEAST 18" deep, most of the time we would go 22-23 inches.
However more important is how the hole is dug (sounds stupid does`nt it!), you want to aim for a nice round hole with around 3.5-4" of clearance all round the post (when its dropped into the middle). When its concreted in you are aiming for maximum support from the ground around the post with the concrete merely there to hold it in place/upright.
Digging a massive "bomb" crater achieves nothing/wastes concrete and in the end produces posts that can easily be knocked over/blown over. The posts generally tend to rock on the massive "lug" of concrete (just like a self-righting toy).
You can try to treat the bottom of the posts (if they are wooden), but generally whatever you do the water is going to lay on the ground and rot the post where its concreted in (i.e. concrete is`nt permeable so the water collected around the post).
However you can minimise this by:
1) concrete the hole right to the top (leave 2 inches for the instant tarmac)
2) instant tarmac around the post, raising the level in a slight slope up to the post.
hope this helps
steve
ps I`ve just done the FIRST fence for MYSELF *woow*, after years of doing other peoples (neighbours, relations, friends and work)
if somebody wants to host a few of my piccies I`ll get a few taken.
what do you mean by breaker? and by medium grinder, is this 
