There is the Heritage trail, but that's just an old railroad grade turned into a trail, it's technically not off leash and it's all private property on the right and left, so you're pretty much relegated to the trail.
I don't know of anywhere in town. We usually hit up a ball field or something for some good play time as the inlaws yard is kind of small. But we're in and out and I have a feeling a large group would attract attention.
That sand bar is great, it's state land on the MIssippi, have never seen a dog on leash there and in the fall it's most likely going to be empty anyway. But that's 20 min outside the city. In the campground itself the dogs are supposed to be on leash, but as soon as you cross the RR tracks you're not in the campground.