On the other hand... Our (usual) posty is awesome! gives the dog treats (although this is probably to stop her from licking him). When it floods (like every year or so), he gets through the water by taping his waterproof trousers to wellingtons and wading through. none of these crappy oh it's going to wet my van door excuses the temporary postmen give! we nominated him in that best postman vote a few years ago. he will also take mail we leave in the flap in the door, and delivers local mail freely if he can.
Just watch out that you don't have your real name/flat number (or any existant flat number, for that matter) on the parcel. People tend to be at least mildly inconvenienced when they expect a free DVD but get a faceful of junk
Go the geek way. Send a box with a GPS tracker linked to a mobile phone that sends you his whereabouts 4 time a day. Having to appear before court because you blew up some chav isn't worth it (yes I have trouble typing this) for even better being labelled a terrorist (the white powder stuff)
Go for the small gps idea. I remember one of my friends got a small gps tracker that sended it´s coordinates when is moves every 5 minutes, for his motocross bike that´s been slightly modified so it´s registered as a motorcycle. The only lock on it is a whimpy chain lock at the front wheel so the gps solution also guaranteed him a good insurance against theft.
Surely a note saying 'We're on to you.' printed in a typewriter font would get the message across. I like the GPS idea, but if the battery goes flat, you've lost it. What about one of those proximity games? You know the ones where you put a little piece of metal somewhere, then you get a handheld thing which beeps when it comes close. You could put the piece of metal in the parcel, and when the beeper goes off, you know its arrived, then when the beeper stops beeping, you'll know when its gone walkabouts. Athough in all honesty, the only place I've actually seen that type of game was on scrubs.
I live in an appartment block and all our mail gets delivered in individual mailboxes on the ground floor which are small. If they deliver a parcel and it wont fit through the letter box they just sit it ontop of the stack. So anyone leaving early walks by to leave the building sees it they nick it. There is always opened mail sat on top of the mail boxes and definatley done by thieves looking for money in birthday cards etc. I have had a few thing go missing and it is rare if they take back to the sorting office and leave a card. My wifes new credit card got nicked and its replacement. The empty envelop was sat on the mail boxes. Its not only royal mail but couriers too. THey will just dump it for anyone coming home to nick.