Probably the best approach is to make being somewhere else feel more natural and appealing - difficult to be specific without seeing the office but I would try:
Place a comfy-looking chair opposite your desk (
angle the chair so as to be slightly diagonal to your desk to signal that it's "open").
If the people visiting you are needing to see your screen then make sure it's mounted on a monitor arm or something similar that will allow you to easily rotate it so that both you and the person in the chair can see it.
If you anticipate that the person is going to be in your office for more than a few seconds smile, gesture at the chair and invite them to "take a seat" - you're then putting them in the subconscious position of having to refuse your polite invitation if they want to not sit there, and in many cultures the majority of people will prefer not to start an interaction on a confrontational note (even a minor one)
workplace.stackexchange.com/users/64903/motosubatsu
You have to ask yourself, why are they going to the trouble to walk around the desk and stand behind you?
This doesn't seem like normal behaviour.
Especially if you've created a cramped and uncomfortable place, moving your desk close to the wall and put in obstacles to stop them coming close (bags, plants on the ground, furniture, coat stand, etc), and maybe followed other people's suggestions to put in a chair or create space for people to stand in front of the desk.
But is there a particular reason for it?
If it's only a few people, why do they do it and nobody else?
If you consider this, then you could work out the specific reason and take counter-measures.
Maybe they don't want to stand by the door.
That's understandable: they might be creating an obstruction, or in the way of somebody else coming in, or in a draft.
Or maybe they are using your office as a place to hide?
Are they wanting to be somewhere nice, such as by a radiator/air-con, or a bowl of sweets, or to look at your desk toys/photos/novelties, or to look out your window?
Maybe being behind you is a comfortable position: they like to lean against a wall, or sit on the edge of something.
In that case, you could put something up against the wall or attached to the wall, or move what they're sitting on, or provide a chair/space.
Maybe they are wanting to see your screen or check up on you.
Consider moving it, or ponder why they feel the need to check up on you.
A less pleasant possibility is it's some form of sexual harassment, trying to lean in close, see down clothing, touch.
(Or similarly, it could be bullying or intimidation by a boss who likes to tower over underlings and physically intimidate them.)
In some cases, rearranging your office will be sufficient, but that isn't necessarily the case (and if they're being sleazy and pressing up against you, narrowing the space will only make it worse).
In other cases, you may have to deal with other workplace issues (trust, boundaries, etc).
Finally, if you really think someone is being inappropriate or is making you feel seriously uncomfortable, it is legitimate to say something.
You could make it light-hearted ("Why so friendly?
What are you looking for?") or if it's more serious escalate it to a manager or HR.
workplace.stackexchange.com/users/94057/Stuart F
What your visitors want, is access.
They don't want to talk to you from the other side of a desk, they want to be on your side, both metaphorically and physically.
So allow for a way for them to come over to your side, without having to walk around to behind you.
Set up your office so you don't face the door, but rather have your side to the door.
Have a chair for your visitor on that side, so the visitor can sit and you can swivel around in your chair to face them.
If you put your monitor on an arm, you can turn it to show your visitor something if needed.
workplace.stackexchange.com/users/18654/SQB
Sit with your back against the wall, as close to it as possible.
Backpack on the floor on the open side will also give them less room.
workplace.stackexchange.com/users/78760/Strader
Have you considered strategic placement of plants?
Most people won't stand in the middle of a ficus spread.
If you really want to make it difficult, get something with thorns or spikes.
A barrel cactus on a stand behind where they tend to stand will dissuade most people.
They can cause injury if you bump into them so if you are a little clumsy or forgetful you might want to go with something less dangerous.
A heavy pot might be a good choice if they aren't getting it and will attempt to move it out of the way.
workplace.stackexchange.com/users/48269/JimmyJames
Get a convex mirror and place it on your monitor.
Works great on the psyche. https://www.newegg.com
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Product/Product.aspx?Item=9SIAHNG7VN3708&ignorebbr=1&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC-
-pla-
-Accessories+-+General-_-9SIAHNG7VN3708&gclid
=CjwKCAjwpeXeBRA6EiwAyoJPKiISqjPJXVIfFo9SERqN4k19R6wbtURt2KCTfwuMPo7uOJcKMu8y5hoCHPkQAvD_BwE&gclsrc=
aw.ds
I had missed the hovering over part and had assumed the offenders were behind OP for which a convex mirror.
But I have a solution for the hovering over aspect as well.
Have a wireless camera/wired camera that sticks on the top of your cube facing outside, towards the door and also capturing activity on your cube.
The immediate response would be for people to shy away from cameras.
Both the convex mirror and the webcam ideas are at my work place and the convex mirrror personally deters me
and I have people talk to me about the webcam as well
(since he is a colleague of mine).
So, I am certain it will deter most folks if not everyone.
https://www.amazon.com/Wyze-Indoor-Wireless-Camera-Vision/dp/B076H3SRXG/ref=sr_1_6?s=electronics&ie=UTF8&qid=1541180803&sr=1-6&keywords=wireless+camera or something like this that runs on battery https://www.amazon.com/FREECAM-Monitor-Wireless-Rechargeable-Security-Surveillance/dp/B075M8JJKB/ref=sr_1_8?s=electronics&ie=UTF8&qid=1541180875&sr=1-8&keywords=wireless+camera+battery
workplace.stackexchange.com/users/94113/Kingkong Jnr
I have my office set up so I am facing the door.  There are several people who insist on walking around my desk, putting them in uncomfortable proximity, and allowing them to hover over me. Is there a way to set up my office to discourage these people from coming around my desk?  I think there must be psychological tricks I can use to make the office space less inviting to them.
How can I set up my office to discourage people from standing behind me?
workplace.stackexchange.com
<office-layout>
workplace.stackexchange.com/questions/121788
workplace.stackexchange.com/users/94055/Lori Petterson
Have your side to the door and place an object on the floor to limit space. You can have your back close to the wall. Make sure your screen can be rotated so they can see it if they need to.  There are a number of options available, including orientating your desk so that there is no need to move behind you or placing objects on the floor, like plants, to obstruct an easy path behind your desk. If people need to see your screen, you could mount it on a rotating arm, and finally, if you really want to discourage any unusual behaviour, you could mount a visible camera in your office cubicle.
You could consider angling your desk to make it seem more 'open' to visitors so that they have no need to move behind your desk. You good simply move your desk as close to the wall as possible so that there is no space behind you to stand. You could place obstacles on the floor, such as plants or a backpack to discourage people from moving behind your desk. If people need to see your monitor screen, you could always have mounted on a rotating arm so that you can face it towards them. Attach a camera that captures activity around your desk to discourage people from unusual activity.