Address the issue. Here is Cesar Milans website.
http://www.dogchannel.com/experts/ce...aspx?WT.srch=1
You need to establish that you are the boss, if the dog is aggressive toward anything else, he is not recognizing that you are in charge, so he is taking over the job of top dog.
Dogs do not understand time out. the only corrections they understand are those given within 2 seconds of their action. time out tells them nothing. Be firm and quick and then let it go.
A firm NO and a sharp nip at their shoulder, just as a pack leader would do, should be sufficient to redirect their behavior.
If you cannot correct it on your own, seek a professional. Aggression will not go away on it's own.