We have 2 dogs we full time with.  One of our dogs is also agressive and we have a sign on the rv "bewhere of dog" he does NOT like people coming up to our rv or other dogs for that matter. I found a dog gadget that I push the button on but only a dog can hear it, for control and  well this helps sometimes.
As far as the flexi-leads we use them along with a short one for this dog.  When people ask is he is friendly we say not always as you will never know how your dog will respond in certain situtations.
You can and usually I do apoligize for any bad manners that my dogs may have when walking them around others.
If other dogs are using the dog areas in the park when we want to use it we simply go the other way or walk in a different area. 
The most important thing for an agressive dog is exercise....as you well know if you have seen Cesar Millan on tv with his show the "Dog Whisper".I am now reading Cesar's book titled "Ceaser's Way".
We also do find that most RV'ers travel with 2 to 3 dogs...amazing!
southwestjudy & Bob & 2blackdogs