Carry a small canister of OC with you on your outdoor runs. I have had to use it several times on aggressive dogs. As a cop, I always had some available, and found that the older CN or CS (tear gas) was not nearly as effective as the newer OC. If it works on Griz, a Rottweiler shouldn't be able to ignore it. I used to run with a handgun after a dirt-bag that I had arrested once tried to run me over while I was out for a run. A later private conversation ensured that there was no repeat performance.
You may want to check the laws before you dispatch a overaggressive dog that is coming at you.
I agree with RIMIC, a small canister of OC. It doesn't weigh that much and will turn a dog in a hurry. We used to pack some when I was working for a utility company, that is until there was a problem with a few going off inside of vehicles and customer complaints. They always got rid of the good stuff.