Lexie and madison have the privilege of going to the park every weekday to play with 5 other yorkies, a poodle, a spaniel, and 2 shi tzu for an hour. its not a desginated doggie park, but for that hour its our doggie park. they run, play, sniff, and get to be dogs. do they get dirty? yes some days. other days no.
I've taken periodic stool samples in to the vet to see if they are 'catching anything' and no they haven't gotten anything put socialized and pooped from all the romping and playing they get to do.
I chalk up their ability to be around other dogs and people in a balanced state due to our daily hour of park play.