There is no "quick solution" in terms of plant material, only structures that you build and then they provide the instant privacy. But its important to decide from where do you want the privacy? Can they see the entire yard? Can they look into your living room or bedroom windows?

I had the same issue with my own home with a neighbor and my best solution was to get one of those 12 x 12 gazebo structures that come with a fabric that goes over the top and also around the sides. Its a nice seating area and provide privacy and doesn't cost an arm and a leg. But in my case, there was only one particular area in my back yard where I wanted the privacy. Being seen inside the house was not an issue.

Another idea is to build a raised planter out of block about 2-2 1/2' high along the area where you would otherwise plant a hedge and then plant Bamboo like Phyllostachus aurea (does well in Zone 7 and is evergreen) which can get to 15 feet but with the added planter height will give the plants a head start. Use a rhizome barrier along the back side below the block wall to keep any rhizomes from creeping across the property line. Water generously. Fastest growing plant I can think of without buying something full grown or a ridiculously expensive giant box tree that you would have to crane in.

Thanks so much for the suggestions! I like the planter Bamboo idea. We have a 6' limit for height on the back fence. The entire yard is exposed which is why I would like to block the view at the fence line.

I'm sorry @kiminpl, what do you mean that plants that grow fast are garden gorillas? Do you mean they ruin the garden? Thanks :)

The plants typically used for screening - trees (often evergreen) and large shrubs - never really stop growing. And fast growing trees never really stop growing rather rapidly :-) So that 6-8 footer at the nursery could eventually be 35' or more in height and almost as wide. IOW, they get BIG!! In fact, the only difference between a "dwarf" conifer and a regular sized one is rate of growth.........if conditions are right, eventually that dwarf could become much larger than what is typical on the tags and in literature. For example. it is not unusual to see a dwarf Alberta spruce, normally a tiny little thing around a foot or so tall at the nursery, grow to be 12-15' tall in time and with a significant spread.

Also, many fast growing trees display unfavorable growth characteristics like weak wood, invasive root systems and malformed branch angles that shorten their lifespans and create garden liabilities.

This is a pretty well recognized phenomenon and I'm pretty sure that was what was meant by being "garden gorillas"!

btw, there are also very cold hardy forms of clumping bamboo - any of the Fargesia species - that can achieve significant height yet do not spread aggressively. They are more like very large ornamental grasses with a slowly enlarging base and require no root barrier or rhizome control :-)

Garden gal expanded effectively on what I meant by "garden gorillas." Choosing plants because they are fast is something one usually regrets a few years later.

Have you considered on of those garden sails that are used to block sun on patios? You'd need posts, but the sails can be single or multiple, and moved to different angles to block the sun (or nosey neighbours) from you when you're in the garden.