I totally agree with LuckyRescue - the dog's job isn't to "protect" his family from perfectly benign people! The no free lunch program is also known as "NILIF" (Nothing In Life Is Free) and will work wonders.
I also agree on finding someone to get some help with him - unless you have experience in retraining an aggressive dog. It's not difficult - make sure you find a GOOD trainer; there are lots of terrible ones! Ask the rescue folks for recommendations.
I am curious why anyecent rescue would allow a dog with clear behavioural issues to be rehomed - for a number of reasons, legal liability among them! I have fostered problem dogs and have taken in Rottweilers (I currently have three) and would NEVER allow a potential biter to go to any but a very experienced home who can prove a committment to working with the dog.
I have had a male Rottweiler in my home for over a year (who I would LOVE to find a perfect home for) but have yet to find a suitable placement! He is extremely dominant, and is perfectly wonderful as long as he understands who's in charge, but he will take advantage of any perceived lack of leadership. He would be a dangerous dog in the wrong hands; that's why I still have him.
Anyhow - good luck....this is NOT a difficult problem to solve.