I can't speak really to the liability issues, but I think that programming is very important to getting people to interact there.
The Evergreen Brick Works has a lot of activities, whether they are for school kids coming in for art lessons and then using the fields as venues or for people growing things on their lands, interacting, and having the farmers' market, or using their new building as an event space. There are ways, through programming, to get people to interact. That's one of the most intensive examples I can think of.
I'm not as familiar with the Rouge Park, but I think there are ways of making people interact, and it's by providing excellent programming that draws people.