Keeping predators out of daily-move pasture pens can be difficult, since predators are motivated and can dig their way into the pen. Some things that help:

• Having a dog close to the pens. I'm told this always works. We haven't tried it.
• Electric fence surrounding the area with the chickens. This mostly works. See my Electric Fencing FAQ. Most people think that electric fencing has to be way more elaborate that is really the case.
• Electric fence wire on the pen itself. Does anyone do this but me? Hammer in a few nail-on fence insulators around the perimeter of the chicken pen, about four inches off the ground, add wire, and attach to the fence charger of your choice -- possibly a battery-powered one attached to the pen itself.

These precautions are fairly effective, but sometimes you get a predator who isn't afraid of an electric fence and wreaks havoc in spite of it. I'll talk about that in another post.