The best recently made up one I've heard is boutros , as in the former head of the UN boutros boutros-ghali , I'll let you work out what it's slang for
much as it sticks in my throat, eagles is right, kettle is definitely a watch , it might not even be rhyming slang , though 've heard it as kettle and hob/ fob as in fob watch, or kettle and cotch, i havent got a clue.
You're right , its st Mary le bow on cheapside , as for boundaries , they're determined by earshot , I suppose it was a lot further before the advent of high buildings , but in recent times I'd reckon the only true cockneys were people born in barts .
Norwood dougie , but if you want to argue who is or isn't a true cockney the I suggest you find out where the bow bells are , anyway I digress , cockney rhyming slang is in my experience most widely used in south London , and south east London in particular.