Ellie41_

Yeah, sleep with your head at the zip, then any fcuker who opens your zip will wake you instantly.

If you have your stuff at the top of your tent, then they'll have to climb over you to get to your stuff, which I'm sure would wake even a deep sleeper.. 

 
I'm a real deep sleeper but my wife suffers from night terrors and constantly thinks people are in our house let alone in a camp site.
If she wakes up in a panic and someone is in my tent (mates or not) they are getting a swift hook in the puss. But i sleep heads up as you say. Solves many an issue. Never had this happen yet but doesn't mean it won't happen.
 
But another option is bin bags full of cans in your porch. Easy to make noise with if you are with someone who can't sleep.

As long as you get to know your surrounding campers, you should be okay (unless they're the thief) because they'd notice anybody strange wandering around your camp.

We try to do this every year, people are more than willing to keep an eye out for eachother  

Oh i know all the people i camp beside. But the wife's night terrors mean either i get hit or someone else does.
Personally i prefer the someone else option

Your wife = your bodyguard at night, it seems...
Fully agree with getting to know your neighbouring campers - we usually have a gazebo with us and other campers around us are free to use it too, especially in the rain - easy way getting friendly