A motion detection sprinkler like those used to deter deer might do the trick.

I'd make sure there is a way to secure it so some pissed off, soaking wet trespasser doesn't yank it out of the ground and steal it.

https://www.amazon.com/Orbit-62100-Activated-Sprinkler-Detection/dp/B009F1R0GC

Easy and cheap would be signs stating NO TRESPASSING, and YOU ARE BEING FILMED.

If it's just a gap, I'd install some posts, or use barbed wire from the adjoining fences, A private property/ no trespassing sign might help. Cactus, bougainvillea, or other thorny plant at the gap.

Barberry might solve your problem.

If it happens so rarely that you've never seen anyone and nothing is damaged, I wouldn't worry about it.

Buy a roll of tie-wire (near the bags of concrete mix at the box store) and weave your own 'fence' across the opening. They'll get the idea. Sometime in the future, you could probably take the wire down.

How large is your yard? Is the grass or ground worn down by those cutting through? Where are they going to by cutting through? It clearly annoys you, but are you being un-neighborly or persnickity? Not daying you are, just something to think about.

If i were in the situation and definitely wanted to stop it I would consider planting already mature bushes at the gap (how big is the gap, anyway anyway?) or adding a piece of chain link fencing.

If the fencing is only chest high, be prepared for people just climbing up and over it if you block the gap.

Plus, keep in mind any potential repercussions if you block the cut-through, if the people are that type.

"Get off my lawn."

Definitely do not get a dog just to keep people out of the yard. A dog needs a lot more care than just a yard to run in. And you really don't want the liability of a dog bite if you know people are entering the property and any dog has the potential to bite an intruder.

Is your yard well-kept or overgrown? If the latter, it might be that neighbors (probably kids or teens) don't realize that there is a new owner who cares about their property. It's not a quick fix, but keeping things mowed, trimmed, etc might help.

You could also plant some shrubs in front of the fenc that would be, uh, unfriendly to land on such as thorny roses and barberry (as other posters suggested). Even if the plants are small, no one wants to jump into a thorny shrub.

A chain link "englufed in trees and shrubery and vines etc. except for one little gap in the corner"

Oh good grief. Go to the big box. Get some fencing wire. Close the gap. The "trees and shrubery and vines etc." will handle the rest.

I read this as there is a gap in the plantings, not the fence. Put the shed there until you are ready to install the taller fence. Or check out clearance plants at bix box nurseries for some inexpensive plantings for now. I wouldn't like anyone cutting through my fenced yard either.

Ohhhh, cooper, I think you’re right. it’s not that there is a gap in the fence, it’s that the trees, etc don’t cover a small portion of the fence. Good catch. I like your suggestions.

I hope that WD isn’t a ”fly-by” poster. This is his/her first post.

Jeez. Really? On behalf of W D, I'll thank everyone who took the time to reply to his/her post.

If these are just the only two isolated incidents that you know of, I wouldn't be too fussed about it unless you discover via your camera that it is frequent. Just block the gap as others have suggested. Lots of options - large plant, planter or pots with tall thorny plants, zip tie some stakes and chicken wire to the existing fence to make it taller....

This is your property and not a bypass. Fences make good neighbors. Put up a temporary fence there and plant a really thorny rose bush.