Nice pics
I'm going to assume that you were using auto focus when shooting through the fence and
I have the same problem when I'm at the races. Try switching to manual focus and see if that helps.
Another thing you might want to try is using a wide open aperture. This will create a shallow depth of field, making the background out of focus and your sharp subject will stand out.
Looks like you're having fun with your new lens. Experiment and keep posting the results.