I always laugh when I heard the 'Pens cause wear and tear to the grass" excuse but these same parks have no problem allowing people to put down mats that run the length of the awning (or more).
I for one always keep my girls on the leash as it allows me to keep them under control at all times. I can not count the number of times that I have been walking them (on their leashes) only to have another dog come running up. If my little one yips my big girl get very upset and has let her feeling known.
If I never hear "it's okay, my dogs love other dogs" while I am trying to keep three or more dogs separate, I will be a happy Camper.