she's NOT going to a dog park, she's just using one
I used to as well. Dogs will be there and I can work on things with lots of distractions. The fence is there as a barrier, but other dogs are clearly visible and distracting.
I would work at a distance he doesn't react, and do what he knows and likes. If he knows sit, have him sit, reward, have him sit longer, reward. If he knows heel, do a sit, then call to heel and reward. But do things he knows, don't try and teach anything new, and work where he is able and get closer as you go.