Guys, you just have to be very aware that all you wish upon somebody has a high chance to impact you or your family. The bag of nails under my truck is guaranteed to produce a nail in one of my tires or one of my friends' or neighbors. Razor blades in the coin tray make me cringe.
I take those as more of "pox on you" responses.
What can you do?
One is to make the process of extracting a cat far more onerous; the street value of RRC/D1/D2 cats is not that high, but accessibility is excellent.
I don't have a good way to post a drawing, but the idea is to get a piece of flat stock - 12GA mild steel or aluminum - and make yourself cat skids.
They won't really be like proper skids, but they'll serve you with a warning if you drag the bottom too close to a rock.
Starting with a 12"x11" plate, you'll end up with a 5"-wide channel with one leg of 3.5" and another - 2.5' tall.
The lower side will go inboard to go around cats, higher side gets bolted to the two bottom holes of the frame crossmember.
The photo above I took while still messing around with the shape - ultimately, they end up bolted using 3/8"-16", 1.25" long, Torx button-head screws, with fender washers and nylock nuts behind the channel.
I have to tell you that sneaking a 9/16" wrench to grab the nuts and keep it while undoing the bolt is a bitch. Cutting this thing off with a reciprocating saw will be super loud, like neighborhood-outside-tile-cutting-job loud, and it will take a while.
In the line of all things biting you in the ass - it'll bite you in the ass all right when you need to get there.
Now, the D1/RRC environment allows you to extend the bent part all the way to the sway bar brackets. You'll need a 24" stretch to do it; I decided against it to keep the cats and things around them cooler.
As you can see, the Y-pipe behind the cats still can be chopped off, so you'll need to make sure the cat is a bitch to remove even if cut off. You have to fashion something in front of the cat - the sway bar brackets and bottom of the framerail offers a great way to make extraction from the front difficult.
Not the greatest solution (it took a lot of embarrassing crunches of the driveshaft against this steel plate, but now it's clear):
All Y-pipes and all Land Rovers are made differently, so you'll have to improvise a little.
You can also use a couple of stainless steel hose clamps around the ports of the cats that are difficult to get to, and leash the cat(s) to either the framerail or the shield you made.
That's about it for mechanical stuff. Now you can get devious with alarms.
This part is pure speculation since I have not moved past buying the parts, but the idea is simple.
A cheap IR motion sensor (board level,
https://smile.amazon.com/dp/B07GJDJV63 , $6.99 for two) and an N-channel MOSFET (IRF520 with driver board -https://www.amazon.com/dp/B07GLNCRR4 , $7.99 for six) should allow you to make something like that:
You need to assemble this little circuit and put it in a small plastic case; mount the case at the bottom of the front bumper aiming the sensor back. The "DOOR LIGHT SWITCH" output of the circuit should be wired into one or another A-pillar's "door open" switches, the rest is self-explanatory.
The idea of it is simple: when a warm body ends up under the vehicle (and cats are already cold), the sensor detects it and triggers the MOSFET to short the door switch to the ground, and the factory alarm will consider it an unauthorized break-in to the vehicle (launching the horns and whatnot).
Finally, there's an even more-untested idea - buy a cheap knock sensor (
https://www.amazon.com/ACDelco-12636736-Original-Equipment-Detonation/dp/B00S0GIUJY/ ), mount it on a cool section of the exhaust system, and feed the signal to a cheap 50-100W board-level amp (e.g.,
https://www.parts-express.com/TDA7492-Digital-Audio-Amplifier-Board-2x50W-320-606 ) hooked up to PA speakers mounted underhood or somewhere else outside the cab. Basically, to announce the act of using a reciprocating saw to the entire neighborhood.
That's about all I could come up with.