After noticing some posts here about stolen cars, is there any reasonable solution out there? Apparently the key diode doesn't really work. A complete electrical cutout isn't practical because you'd have to keep resetting the clock, etc. so any ideas?

 

Car and home alarms tend to lack the respect/attention they used to get.
In past similar discussions, many would say "if they want it bad enough, they'll take it anyway." They would argue that thieves use a "roll back" and take your car, never to be seen again. Some even commented they don't secure their vehicles for that reason, which is really enabling the thief to make his crime easier.
Personally, I believe in layering of protection...especially since the state I live in has been for years the car theft capital of the USA. Cars can be across the USA/Mexican border before the owner is even aware of the loss and the metro Phoenix area has at least 2,500 documented gangs known to law enforcement. CA residents are even more versed in this than AZ.
Most common everyday car theft is done by joy riders, not a professional. It's a "crime of opportunity" where the thief is usually looking for the easiest car to steal. An owner fails to use basic precautions...lock the doors, roll up windows, keys in the ignition, park in a high traffic/well lighted area, car not in sight of owner, etc.
Corvette owners also tend to park their cars out away from other vehicles. A "crime of opportunity" thief wants to bring as little attention to himself as possible. That's easier done with other cars around to conceal his actions. Car thefts by joy riders are usually found, albeit in stripped or damaged condition.
The streetrod industry responded to the same issue years ago. They are a number of products that can be adapted to more modern cars.
A mechanical disconnect switch (bottom image) can be used to disconnect power from the battery. A 16 gauge wire jumper can maintain power to accessories.
Three companies, HOTRONICS (hotronicsproducts.com) or WATSON'S STREETWORKS (watsons-streetworks.com) PAINLESS WIRING (painlessperformance.com) manufacture/sell a wide selection of electrical/mechanical solenoids/switches. They're made in the USA if it matters to you.
One particular product has a miniature toggle switch (below image). With the switch hidden and activated, it prevents power from the battery to the ignition. It might be just enough to encourage a thief to move on to the Honda parked next to your C5/Z06. I prefer these type of switches over the "quick disconnect" type attached at the battery post. I personally have had the quick disconnect come loose with vibration.
The product also has a small gauge wire and inline fuse which maintains power to memory features. A small 16 gauge wire jumped across two terminals is sufficient to maintain power to memory features, but will self destruct if someone tries to start the car.

 

Thanks so much for the info. It took me a couple days to get back and view it. I like it. I will look into getting this. In the mean time, I bought a club type thing for the steering column which locks across the column and airbag and I also bought a club type thing that locks the brake pedal to the floor which ends up locking the shifter as well (A4). I really hate carrying all this crap around so it will only be in those rare instances that I leave the car unattended for more then a few minutes and until I can implement your recommendation.

thx again!

 

I put a GPS system in that sends text messages to my phone if there's any unauthorized movement.

It also sends text messages if the battery line is cut or if the voltage drops below certain thresholds I've outlined.

The system has it's own battery too for when (if) the vehicle one is disconnected. (ie a thief cutting the battery cable and putting the car on a flat bed)

If there is any unauthorized movement, I can log onto a web site from anywhere and track it. I can even track it with my laptop from another moving vehicle.

 

Interesting setup. Can you provide additional info on this?

 

What would you like to know?
There are lots of different providers of this type of thing.
They all have their strengths and weaknesses and slightly different feature sets.
Mostly it's meant to be used as an asset tracking system, but this particular company's product and software features enabled me to utilize it as an early warning and monitoring system.

One popular and slightly similar system is LoJack. I don't know much about it though as it's only in the States (I'm in Canada).

Feel free to PM me.