Fixing edgings

[keredwh]

Just removed a bit of useless lawn at the side of the house and want to gravel it. The neighbours drive runs alongside it and there are flush edgings with haunching under where the lawn was to stop the drive collapsing.

I want to put a raised edging down the side too which will sit nicely on the existing haunching but I'm not sure how best to fix it. Should I just sit the new edgings on sand? Provide them with their own haunchings or bed them on some mortar?

There will be no weight bearing on the gravelled area so no great strenghth required. What do you experts suggest?