I planted a hedge of arctic fire red twig dogwood a few years ago in clay soil that is easy to maintain at four feet. It fills in real quickly, and has small white flowers in the spring. It has nice winter interest as well. Another couple suggestions would be privet and barberry. If you want something to retain color all year long, you might want to try a hedge of arborvitae. You would just need to top the shrubs off when they reach a desirable height. The only other plant I can think of would be forsythia (which is very pretty in the spring), although I have heard that it is somewhat difficult to keep tidy as a hedge.

Forsythia is indeed difficult as a hedge. If you try to keep it in a box shape, it looks ridiculous, and if you let it grow as big as it wants to, you lose several feet of your property and have one week of glorious bloom and annual pruning out of the old wood. My parents had a 100 foot hedge of it and boy, was it a pain.

one person's definition of ridiculous can well be another's definition of beauty. One person's definition of beauty is another's definition of an eyesore.

What kind of vine? I ask because vines are going to be a pain in the butt to maintain a clean hedge, so I'd select something where the vine can grow and blend in...which would generally mean, no evergreen, you're looking at deciduous. But the options are potentially endless.

Spirea, potentilla, dogwood, currant, larger growing perennials like certain grasses, baptisia or rodgersia, viburnum...the list just keeps going.

A picture of the situation would be useful. i'm trying to imagine a tangle of vines keeping to their side of the hedge. Could end up a complete mess unless you plant the hedge well inside the property line so you can mow behind it. And do you really want a hedge or a mixed shrub border?

Good question, floral. I could do a hedge OR a mixed shrub border. I'm open to any ideas.

I will also post a picture in a moment...

As for the vines, they are a menacing cocktail of trumpet vine, wild grape vine, raspberry, and some other nasty evil useless vine I don't recognize. It's like someone asked themselves one day what might be the nastiest assortment of garbage growth they could assemble, and then set about creating it. And yes the vines will want to entangle themselves into and consume whatever I plant there. But i will just have to stay on top of cutting the mass back to the border line periodically.

Here is a picture taken before the spring flush. The big thing growing up from the bramble is an autumn olive (An invasive specie. It was not 'planted there', but is basically a weed that found its way to mature adulthood. Like the vines, my neighbor "likes it".) The vines don't look too unsightly in this image, but when summer arrives, they double in volume and look very ratty.

It seems to me this situation calls for a hedgerow, which may be what your neighbor is thinking but you can still enhance in aesthetics. it is probably serving as a vital wildlife habitat. You have a beautiful property and prospect. The beauty of it is the continuity of the two open properties. Don't spoil it by creating an anomalous barrier. Is there someone who can describe a hedgerow concept and its maintenance? Maybe one of our British posters?