Neighbour climbs over the fence next to my house to get home.

@AveryC so the people are jumping the fence instead of coming through the middle? Contact the developer and tell them people are using your garden as a short cut and ask what they can do about it. It may not be clear they are entering private property and yes, they are out of order using your path/garden as a short cut.

Mahonia is spiked.

Win! That means you can attach trellis etc to it and make it much harder to jump over.

Looks like a poor design. Developer should have made it so people could take the sidewalk to their own homes.

Get the developer's word in writing. Before you add a trellis or replace the fence etc. You'd never know who will come back at ya.

Brilliant!

Huge high fence then 😍

That’s excellent news that the fence and boundary is yours, so you have control over it, so OP what do you plan to do?

As many previous posters have stated just grow a spiky hedge along your fence. Very unpleasant to over.

Natural deterrents are completely legal and while you may need go keep the height and width down they can be legally taller than fencing.

That's great OP. You and your neighbour could agree on a joint fence that covers both your properties.
If not, make yours higher.

That’s normal.
Everyone fence is a boundary to something, road, path, someone else’s garden.
They gave you ownership so you have to maintain it.
Now you can both put up huge sign saying
no trespassing over this fence, private property.

The trouble with signs is they often get vandalised, removed or just outright ignored (what sign , I didn't see a sign etc) so physical barriers are the best way to go really

Spiked at the top of the fence and a warning sign.

Couks you use anti climb paint for the fence? Or vegwrable oil which dries leaving a sticky residue?

Lots of signs saying private property no trespassing. Sign on fence saying this is a fence please do not climb.

I was going to say this. A nice holly hedge. Or Berberis,

The simplest solution would be some signs on the low fence "Private property - Do not cross this fence".

Then if those don't work, I'd go tall, trellisy and spiky.

OP, on the picture where you added red, can you explain what the gap is between the two black areas that you also drew?

Assuming you added the black lines to indicate your and your neighbour's boundaries, why is there a little gap between them?

I know you said the red area is co-owned, but I'm curious about why there would be a little gap marked out between, what I assume are, privately-owned areas.

OP does own the area they are jumping into. That would annoy the hell out of me too. I m obviously made of sterner stuff though because everyone who did this would get short shrift from me.

Ok so there's a low fence on the edge of yours and your neighbours property. In between your houses is your access to the road. People are viewing this as a public right of way.

Yes this would annoy me and I'm not sure plants would work as they could climb over further down. Have you spoke to neighbours about it?

I'd ask the developers to put up a higher fence or speak to neighbours about a gate if possible?

I think I get it.

You're at the end of a cul-de-sac.

Your cul-de-sac meets, but is blocked from, another thoroughfare (not sure if its a road with a pavement or just a footpath) at a right angle, and is fenced off from that thoroughfare.

People wanting to access your road will hop the fence and then walk up the road a bit, rather than walk all the way round and in from the actual entrance to your road.

The issue here is caused by lazy developers/planners - people will follow 'paths of desire', usually the shortest possible route from A to B.

Planners are meant to understand these and keep them in mind to prevent exactly this sort of issue, but in between the 'drawing up plans' stage and the 'making contractors actually build it' stage... shit gets tossed aside and forgotten, if it was ever there in the first place.

Look at your deeds, get your neighbour to do same.

See if you can increase fence height (probably not), or plant something your side of the fence that means hopping it is not pleasant. This is more likely as typically developments only want to manage planting/landscaping for a short time. Usually the time it takes for the development to be finished and all sold off.

Plant something that grows pretty dense and spikey, you may well need a temporary fence as it grows and you may need to shell out on well established mature plants or small ones will get trampled by the trespassers.

You probably can't use anti-vandal paint on the existing fence, however you may be able to use it on your own inner fence, should you put one up, HOWEVER... you will need to ensure it is marked down its length at regular intervals, as being treated with anti-vandal paint, or you may be liable for damage to peoples clothing/property!

It would have been better for them to put a gap in the fence right in the middle of where the two parking areas join, and create a right of way there, so pedestrians would then take that path, rather than jump a fence further up/down, however that then means selling properties that have a ROW across them which puts off buyers...

OP and her neighbour opposite own the area between their parked cars and have shared access
It’s their private land

Seriously
A fence is a barrier
If people were allowed to walk that way there would not be a barrier blocking access.
They are taking a short cut because no one’s stopped them yet and they are lazy.