Yes, unfortunately one's own dog can be as bad as any other predator. Tufnell has tested out your fencing for you, though, Col, and I'm so glad Bluebell is safe. Bluebells are known to be a relatively shy and timid breed, so I'm not surprised she was the one who panicked worst. POL pullets do take a few weeks to settle in to new surroundings and once they've learned their way around and begin to lay, will be much less inclined to fly. But training a young dog to ignore them is very difficult, and from my own experience the only way to be safe is to keep them totally apart. My Poppy has started teasing the hens through the run wire since I got my two newbies 3 weeks ago, because they get in a flap when she yaps at them. The older ones had learned to ignore her, but for the time being she can start them all off, especially the leghorn pullet. If she could get in to the run there would be a major panic and probably injuries or deaths, not because she's aggressive but because she's a lively young dog and her prey drive is easily activated when it looks as if they're such fun! Our previous terrier got out in the garden one day when the hens were loose, and met one face to face on the path. He was just gathering himself for the kill when she gave him a really hard peck on the nose and he fled, crying. After that, he pretended not to see the hens at all, lest his dignity was hurt by such a redoubtable enemy. Unfortunately I've never worked out how to safely engineer this occurrence with Poppy!