Female Shepherd Aggressive and Nips

Question
My wife, twin 7-year old daughters and I own a 14-year old male Australian Cattle Dog and a 1-year 9-month old female German Shepherd.  The Shepherd is very aggressive and even nips some strangers when they come to the house.  Can the nipping be broken? It must be, or we need to explore alternatives.  Too many visitors and children in the neighborhood to live in fear about who may come to the door and whether or not our Shepherd will like them, or will act aggressively toward them.  She also seems to be generally very high strung---lots of submissive urination with me (husband/father) but not my wife.  I must greet our outside every morning / evening, otherwise she will greet me with a little piddle on the carpet.  Any advice would be GREATLY appreciated.  Thank you very much.

Answer
GSD's as their name states, are herding dogs and as such , like aussies use their teeth to control people and situations. Get your dog involved in obedience classes, walk her twice a day BRISKLY until she's tired. Get her some toys that make him use her brain, such as kongs with treats stuffed inside. At least twice per week she needs to work/run/play until her tongue hangs out. Have her spayed if you haven't already. Unfortunately some bloodlines of GSD's are just as you describe and need proper guidance and training. Obedience training and establishing proper pack control will increase her confidence and help with the submissive urination as well. Do not ever scold her for doing that. At the end of this post I will include weblinks that address both pack issues and submissive urination. The high strung behavior is in part due to lack of security in her pack and to lack of exercise. When she nips. cup your hand like you're holding a coffee cup , turn it sideways and give her a sharp nudge on the collar area with it, not a HIT , just a nudge , making a loud strong CHHHH noise (like the beginning of the word chair) and say NO. She is still a young girl and if you train her correctly you should be able to have a lovely pet.
Go to Alpha Boot Camp , you can type that into your browser or use this link
http://www.sonic.net/~cdlcruz/GPCC/library/alpha.htm
The information on establishing pack order is spectacular
also go to
http://www.ahshc.org/bhv_suburination.asp
where you will find a lot of helpful information. If you are able, buy Cesar Milan's book The man is nothing short of a genius when it comes to dog behavior
Cindi