I think trip wires, flares etc are all great. A few more ideas off the top of my head:
Instead of making the easy route appear too hard for them, make the easy route appear even easier. What you don’t want is an obviously impregnable driveway, so that the enemy could hop the fence and come in from 360* that you cannot guard effectively. So make the ingress appear easy. OTOH, the driveway might appear “too easy,” (suggesting an ambush ahead) so also think of the 2nd and 3rd and 4th easiest infil routes. That’s where you set your dead falls, steel bear traps, pungi pits etc. With shotgun and flare warning devices, etc. Of course, somebody with their leg in a bear trap will do a lot of screaming, so the audible alarm is redundant! Bear traps are pretty cheap, require no electricity etc. Buy them now: they are much more effective than home-made “survival” type snares etc. that you will have to make once the stores are all closed.
There are some fast-growing thorn bushes that are almost as good as triple-rolled concertina, but appear totally natural. You can even take cuttings of thorny “pest plants” that nobody will miss. The thorn hedges can be arranged to channel infiltrators into your kill zones. They won’t know they’re in a kill zone, until they are.
You can even erect a razor-wire fence, and THEN plant the thorny hedge over it. The razor wire won’t even be visible. (A visible security fence can mean, “something valuable over there!” So hide it inside of natural-appearing thorny hedges.) Natural-appearing thorny hedges can be grown in Y-shaped channels, to guide the bad guys right into your traps or ambush zones. Since they appear to be natural growth, nobody will suspect they are being guided into your killing ground.
Old tech can be very effective. Pressure pads under the driveways hooked to a silent alarm are undetectable and can run on just a little solar juice. Anybody driving a vehicle up will announce his coming in advance. You probably already have something for a vehicle alarm. It’s just a question of matching it to solar power. Ditto motion-detectors, but they have a much higher false alarm rate. You don’t want one that will go off for every deer, stray dog and waving tree branch, or you will soon learn to ignore it. A pressure pad will only go off for one thing: a vehicle.
There are tons of more ideas like these, but these came right to my mind.
My husband calls blackberry brambles ‘redneck concertina wire’. Raspberries and possibly dewberries would work too. As long as they had thorns and were suited to whatever climate you particularly have. Check the local extension office. Disease resistance is a big plus. If TSHTF you don’t want to run out of spray one year and have a giant dead wad of stuff in the yard.
Added bonus, brambles are idea hidey places for snakes. Like the castles of old had moats with alligators, redneck castles can have thorny brambles with snakes! So, don’t put them close to where your kids play.
Oh, and if you order something from a nursery (or even if you don’t), once a year for several weeks you can put on your anti-snake-clothes and pick gallons and gallons of fresh fruit. Yummy. Delicious AND devious.