Jack's Lake is before Sandy Lake Dog Park. It is privately owned by the Annopolis Group, and so far they have not put any restrictions on hiking, biking, and dogs off leash.
Go down Smith's Road, and look for the gate for Jack's Lake. If you come to the dead end you have gone too far, but it doesn't matter. You can also part at the last gate as there is a foot path through the woods that will take you to Jack's Lake trail.
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