It's a problem alright.
Do you currently have any kind of fencing along the property line?
How wide of a hedge are you prepared to grow?
I've been thinking along similar lines and researching. So here are some ideas for starters:
I suspect these are for much wider spaces, but here are a couple of websites I've been looking at:
Trucs d'artan Ã¢â‚¬â€œ The Woven Hedge
BCTV Handbook Online Ã¢â‚¬â€œ Hedging
In the first link, there are links to "The Fine Art of EspalierÃ¢â‚¬â€œPart I, II, and III" in the list to the left. You might want to check those out too.
Here is a list of shrubs/trees that are recommended for espalier:
For some reason, this list doesn't mention some fruit trees and berries mentioned elsewhere: Sweet/Pie Cherries, Peaches, Nectarines, Plums (all recommended pruned in FAN shape); Brambles, Currants, Gooseberries (all can take some shade, especially currants and gooseberries). Also, you CAN grow hardy trifoliate orange in espalier. Some varieties have limited juice that is not
sweet but can be used sweetened like lemonade and the peel can be candied.
Obviously, the above ideas will need to be tailored to your region, preferably limiting selection to mostly native species for best wildlife value.
If you decide to go the espalier fruit tree/shrub route, I recommend you look into permaculture and plant guilds, and plant insectary, nutrient accumulator, etc. plants in the understory.
And for sake of completeness, this is what I'm planning for one part of my back property line, although these are not plants, and I don't know if you have kids.