Thanks all for the massive amounts of ideas to consider. Figured rather than having a million posts quoting each I'd get one big post trying to cover all the points raised.
SJ
A battery isolator is always handy on old cars anyway to prevent ropey wiring draining the batter and would be a nice and easy one to install. My main issue is it would be difficult to locate the break in the wiring somewhere hard to find, it would need to be very close to the battery and as such a semi experienced theif would know to check for it (once they had sussed there was nothing going on). Totally take your point though, anything that extends the time it takes them to get the car going increases the chance of them giving up, they don't want to be sat there longer than required. Plus anything which forces them to open the bonnet is likely to draw attention, even if it's from helpfull passers by seeing an older car broken down at the side of the road!
I prefer the Jack Russell to the alarm idea, in part as I understand how they work better than I do alarms

(more on that later), though I'd prefer to take the little fella with me than leave him in the car!
LPrescott
Love the idea of the switch to set off the horn, though as with all these things some positives and some negatives.
-Draws attention to thieves, people beeping horn for extended periods of time more likely to get attention than alarm. An alarm goes off everyone tuts, a taxi beeps it's horn outside and half the street look out to see what is going on.
-It means if I get in the car, forget I've immobilised it I know straight away, no time sat there wondering why my car wont start!
-Disadvantage is potential thief knows somethings up and as horn will be wired in could chase wires back and find the switch. Another option might be for the switch to turn on fuel warning light and cut power from the fuel gage... theives might even go and get you a free can of petrol! Realistically though this is extra complications which could cause more issues. Keeping it simple would make it less likely to cause an issue and hopefully even make it harder to locate.
Cameron
Simple but effective I like it! Not sure I want this as my long term security solution but until I've got one I may well go with it, will have to check if their is a fuse in the cabin for the fuel pump on my Panda!
Portland Bill
Removing rotor arm would hopefully stop the least knowledgable thieves and as per dragon mans point any swapping/removing of leads would slow the process down generally.
My car is fuel injection so I recon interferring with the pump is likely to be the simplest and most effective method (they could get it around the corner on the starter motor but hardly a joyride!). For non fuel injected cars, though a fuel tap would be effective it could as mentioned on here be a cause of leaks, plus either the fuel line would need to be brought into the cabin or the tap would need to be external, so not easy to opperate discreetly.
I did read somewhere that tidy cars were much more likely to be nicked, I'll use that as an excuse for the state of my volvo

, though the Panda is staying neat and tidy!
The broken down sign could potentially work for a night or so, concern there would be it would potentially make it a bit of a vandal target for local kids. Broken down old car to play on/set on fire... in that respect I'd rather it looked cared for!
I agree re alarms to a point, ignored and often tempremental. The alarm in our old van served two purposes, annoying everyone and draining our battery!
Kolza
I take your point regards public form, is there any way this could be discussed privately amongst forum members only or are all threads on the forum public by nature? I'd guess as long as we do not get too technical in terms of locations of immobilisers etc. we should be fairly safe, plus as has already been said, the type of theives after a Panda are more likely to be opportunists than pre planning career criminals. Certainly in my case I'm not really worried about my regular storage location as it would be a lot of hard work compared to cars out on the street, plus if you really tried joyriders would probably take my bike and theives after money my tools rather than the Panda.
FDNY21
I agree a visual security device in addition to something more discreet is definitely a good move, even if they don't manage to take the car the damage caused in the attempt would be gutting! There are a load of different steering wheel locks on the market and I'd be interested in any advice as to what works well with the Panda and what would be the most secure. One issue with this sort of device is storing it when not in use. I had one for my old Saab and it didn't fit under the seat very well and was always in the way when I had passengers in the back. Given the size of the Panda and the length of trips planned storage will be at a premium so a crook lock would have to fit neatly somewhere?
Dragon Man
Taking the ECU out would certainly stop them, even if you put a sign on it saying 'no ECU so don't bother) I'm guessing most theives don't carry a model specific ECU around with them! Issues I can see here are:
-Carrying an ECU around is less than ideal
-ECU might get damaged while out on travels.
-I've had an issue in the past with the connector pins for an ECU being damaged and guess constantly removing refitting could cause wear and issues.
In short this would be a great solution for long term storage of the car, but maybe not for each time you part up somewhere on a daily basis.
Don't suppose anyone could PM me the route and colour of the power cable for my fuel pump
. Also I'll need to work out what rated switch to get for it so any tips there would be welcome.
Thanks all for the great input, we don't have to make Panda's inpenetrable, just more secure than the Nissan etc. we park next to:slayer: