You will most certainly learn (as I did) that as your dog/bitch ages that dog parks are not all they are cracked up to be. When I used to live in Edmonton what would infuriate me the most was that all the owners would be standing around chatting, not watching their dogs in the slightest and then some little football sized dog would run up with an attitude and try to pick a fight with my big guy. Nervous laughter as the owner would run up to pluck off their little aggressive mutt which was dangling off of my guy's lip. It would happen daily and eventually you just stop going....or in my case I made it a special point that IF I wanted to give my guy a great off leash run we would go the off leash park extraordinarily early to stave off having to deal with idiot owners with overly aggressive dogs.
I knew that the day had come to stop going when my normally friendly placid boy would stiffen and hackle at the approach of a yippy smaller dog racing towards him.
When you're the owner of a large breed dog you have to expect that even in cases where an attack is fully provoked by the smaller dog that it WILL be your dog blamed ~~ perhaps not legally or by the authorities ~~ but certainly if it hits the media the headline will undoubtedly read something to the effect of ROTTWEILER MAULS CHILD'S PET. I'm sure we have all experienced the effects of negative press about our breed and it is blase attitudes like "it won't happen to me" that perpetuate the problem.
In my opinion you are setting your dog up for failure by continuing to use an off leash park after you have seen these behavioral changes occuring in your dog. To this day (and I'm thankful beyond belief that we bought our own 160 acres of doggie paradise) my old guy does not like little dogs which certainly wasn't the case in his early socialization. I think what everyone who isn't an off leash proponent is trying to say is WHY subject your dog to these negative experiences that may harden his/her attitude to other dogs in the future, unnecessarily?
My one girl also hates other dogs as a result of being tumbled by two overly zealous weimaraners when she was only a baby......the effects are lasting but thankfully my younger rotts have never experienced off leash parks and have only had the positive experiences of other dogs belonging to friends/relatives and in training classes.
While not even TOUCHING on the amount of diseases (vaccinated or not) that your youngsters could pick up from an off leash park.....that would be a thread in and of itself.
JMO
Heather Peters