People determined to walk there will just trample your new planting. Put up a sturdy fence.

the evergreen barberry Berberis 'William Penn' is not quite as tall as you may want, but it is tough and spiny enough to be a deterrent, as are many listed by Forest Farm, out West. They are on line and describe each sort they have. I found the hetzi type Ilex, or Holly is similar in general appearance. But a mixture of many sorts would be endlessly interesting. Many not evergreen. Like burning bush, Buddlea, Viburnum, Aronia, hawthorn and Rose of Sharon. Some Rose of Sharon and Buddlea will not produce seedlings are are worth seeking out.Evergreen Viburnum exist. Not evergreen, but almost faultless are the Knockout Roses.
All will need protection from trespass until they become so big that they matter. And I would be held back by the cost.

Thanks bogturtle, I'll check these out -- I particularly like the idea of some barberry mixed in.