Rocky is not aggressive so a bold smaller dog would be fine but a lot of smaller dogs will bark and run, and the moment there is something to chase that hunting instinct kicks in, I would not want him to chase and grab a little dog because even without aggression he could do a lot of damage. We are careful to introduce him to little dogs when we take him to dog parks, the bold ones we are comfortable letting him off lead. Around here you do see it a lot that if there are big dogs running around the dog park the owners of little dogs won't enter. For social play time we prefer to have him play with dogs closer to his own size so there are no bite size accidents.