This is something I have been wondering too.
I live in the city and board my horse just outside, and we have a lot of public beaches (Great Lakes area).
Most of them are posted no dogs, so obviously I know I cannot bring my horse to those. But what of the ones where dogs are allowed? I think if you ask anyone from the town office, their gut reaction would be to say 'no, not allowed'. So I wonder if instead of just asking some clerk if they are allowed, maybe it is better to ask to see a copy of the bylaw where it is written that they are not allowed. If it cannot be produced, then my guess is that they cannot stop you.