The dog shouldn't be getting into fights or that is what it will consider normal and out the window goes the socialization.
The problem with dog parks is the dogs begin to consider the area as their territory and are more likely to fight. If it is getting in a fracas with am bulldogs then your dog can easily get beating and killed.
On trails, when the dog meets another dog, the chances are that you will be going a different direction to the other owner and the dogs are in transit and consider the area a neutral territory. So they'll have a sniff maybe a growl and be on their way.
If my dog was getting in a fight in a particular area I'd avoid that area in future. It is not good to have an dog aggressive dog imo.