Either measure to the top edge, or measure to the "riding line", but plan out the radius for the turn. I often use a rake held outstretched (or a tree branch if the rake isn't long enough) to get an idea of where the curve will be.
You just keep dumping dirt and raking it into shape and packing as you go. Dirt needs to be damp, but not muddy, in order to pack correctly.
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A lot of people use flat head shovels to pack, in addition to foot stomping, or even hitting with a 2X4. Unsecure image, only https images allowed: http://a1.espncdn.com/photo/2011/0630/as_bmx_trails1_576.jpgUnsecure image, only https images allowed: http://img.photobucket.com/albums/v157/pnj666/fivemanberm.jpg If you spend a lot of time dampening and wetting the flat head shovel, you can get ridiculously smooth shapes. Unsecure image, only https images allowed: http://canyoudigitbmx.com/wp-content/uploads/2014/05/IMG_6047.jpgcanyoudigitbmx.com http://forums.mtbr.com/urban-dj-park/i-need-guide-pump-tracks-968669.html