evergreen honey suckle is a nice suggestion,its a climber but it is slow growing so easy to prune and dosent get out of hand.

what about thyme, they are hardy and if you do stand on them then they wont mind and the smell will be lovely. There are lots of different types.
you could also consider some of the smaller dianthus too.

Will thyme be OK on that soil SBG? Its hard to think of something that fulfills all those requirements. I'm wondering if a row of tough low growing evergreen shrubs might be enough to stop people walking on the border? An alternative might be to grass most of it and put a small shrub at intervals, and you could then tread in the spaces?

How about cotoneaster horizontalis? It's tough as old boots, can be stood on, cut back any time you like to any size you like, is evergreen and has berries the birds love.

well as thymes grow in scree conditions as well as soil in the med areas I reckon it will withstand it. some NT gardens use it in areas that have a heavy footfall as it is tough.

Helianthemums come to mind - they'll be fine in that sort of environment, otherwise Campanula portenschlagiana (also called C. muralis), Arabis procurrens, Iberis sempervirens. All are evergeen and low growing, all flower. Silene schafta flowers later, is semi evergreen. Lavender 'Munstead' makes a nice low growing hedge, but will need clipping over twice a year and replacing after 4-5 years when its got leggy.