There is a city about 100 miles from here that allows dogs into their wilderness areas. They even allow off leash activities on dirt paths. They do charge a couple of dollars per dog upon entry.
The few times that I have visited those parks I have encountered the best behaved and well-socialized dogs. I think that this small fee might discourage irresponsible dog owners. People that don't care enough to properly train and socialize their dogs will probably not be willing to pay an entrance fee. It is a way to help weed out the trouble makers.