Please note that hitting a dog with a newspaper or anything is not a positive training technique, and as such discussion of it is against BoxerWorld rules. Please refresh yourself of the rules you agreed to when joining here:
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Using physical punishment (corrections, whatever you want to call it) with an aggressive dog will only tend to increase the aggression. There are several other, safer, ways to deal with the issue.
To start with, what kind of obedience training are you doing? While I think that the dominance theory is a bunch of malarkey, you do need to establish yourself as someone that your dog can trust and rely on, both for setting guidelines for daily living and in the case of threats, emergencies, illness, etc. You need to work with him on letting you grab his collar - a very threatening thing for a dog - and on resource guarding.
www.pawsitivesolution.net has some good information on resource guarding (and probably the other, as well).
Putting him in a down is not a bad idea, but telling him "no" after you do is counter-productive. You've just told him he's a bad boy for obeying your down cue. Regardless of what he did 2 seconds earlier, if you ask him to do something, you cannot correct/reprimand him after he does it. This is the same reason you cannot call a dog to you to punish it - pretty soon they learn that coming to you means Bad Things for Dogs and they won't respond. A solid leave-it and/or recall cue would have worked in this instance, so these are also things you can work on.
