Part removal of concrete?

I'm going to start putting up a fence soon. The boundary is not mine so it'll be on my side of it, but there is one privacy panel 7ft from the starting point. Next door's garden is about a foot higher than mine at that point so where the posts have been concreted in, I have two ragged chunks of concrete sticking out over my yard!

They don't stick out far but I want to put my fence flush against the edge of my yard (which is concrete slab, I'll be using bolt-down post supports for that bit) so I'll need to chip a couple of inches (at most) off these ragged chunks to fit my panels neatly. It won't compromise the privacy panel in any way, it's very solidly done, just not neatly on my side.

What's the best way to chip the excess off these chunks? They are heavily pebbled too.

Also while I'm here... could anyone advise on how much postcrete to use per 75mm fence post in soft, sandy soil? The yard itself is only small, I'll be doing 4 panels on there then it's lawn for the rest.

 

If you haven't got a breaker then a Scutching hammer,

http://www.screwfix.com/p/forge-steel-hickory-handle-scutch-hammer-20oz/78159

You'll need the combs underneath too, they go in the ends.

don't forget safety glasses too