I am aware of this kind of methods. There exist several variations. That's why I said "can not be read with an ISP". You said it could be done but obviously you had the same kind of methods in mind. Seems that this was kind of misunderstanding.
To make the point clear to the others here: the "security" of the fuses depends on the value they have to protect. If they serve to protect casual copying they are to be considered 100% secure. If they serve to protect against a determined and knowledgeable attacker forget it. No *standalone* device today (and probably none in the future) can be hardened to keep a secret against determined attacks.
I am aware that there are techniques to harden devices even against invasive attacks. However as to my knowledge this makes attacks more costly but not impossible.
Beginners might want to have a look at one of the standard books:http://www.cl.cam.ac.uk/~rja14/book.html