I think the problem isn't so much that some dog owners are irresponsible (true), but that most dog owners are conscientious. They take their dogs for walks every day. Moreover, the demand for off-leash areas is sky-rocketing throughout North America. No one wants to admit that their enjoyment of nature is harmful, but natural areas can't tolerate high traffic levels, whether pedestrian or wheeled. (If you've been to the off-leash area of High Park recently you'll see what I mean, but even on Hawk Hill, where I whiled away many a happy hour this fall in the company of some of the most knowledgeable people and generous with it too, the grass where we were all standing is gone and the soil exposed.) Our natural areas are overloved.