I share your concern, although he clearly has very professional security in a pretty secure neighborhood. I should emphasize that FReepers only found out Rumsfeld's address from the left's announcement of their plan to protest there.
I also repeat that it's just bad form to protest at somebody's personal, non-official residence unless the object of the protest is hosting an event that is being protested such as a fundraiser bringing outsiders to the neighborhood.
A different organization of leftists went to Karl Rove's personal residence about a month ago. They trespassed in his yard and surrounded his house with people banging on the windows. Rove was home, as were his children.
Police arrived and moved back the leftists. It was an ugly scene that should have had dozens arrested, but DC juries likely would have nullified the law and let the trespassers go. I don't think that the police arrested the window-banging trespassers.
Is it possible for anyone to drive down Rumsfeld's street? Would it be possible for someone to toss an object at his house that would actually hit it?