Keeping the walk as interesting as possible will help avoid frustration. You can attach a long line to a harness to give your dog more freedom to explore. Allowing them to follow scents around the park and taking a dog-directed route could be fun for both of you. Playing with a toy or scattering treats for them to find will also keep their brain active.
You can also practice training exercises. You can reward your dog for turning and coming to you even when they’re on-lead. This will help establish a good recall once they are off the lead in the future.
If they are off lead, then keep rewarding your dog for coming when you call them. Even if you’re the only ones about, someone else might appear at any moment. It’s vital to be able to call your dog back and pop them on-lead if you need to keep your distance from anyone.
If your dog enjoys a reward for coming back to you, they’ll be more likely to come running next time you call. Take treats that you dog loves with you on walks.