Help! My dog has become a chicken chaser!

I need help! We adopted Duke last year. He is a lovely, wonderful weimaraner dog. We have 4 point 77 acres in the country that is fully enclosed with 6 ft chainlink. We have 35' x 45' dog run with dog house that he shares with a dobie and a lovable mut while we are at work. When the first person gets home, they usually let the dogs out of the pen, give them fresh water & play with them. Then the dogs have the run of the property and the birds and rabbits all know to disappear. When I get home later in the day, or if the weather is bad, they come inside, eat, and lay around on their people. In nice weather (down to 40*F up to about 90*F) people and dogs then spend the evenings outside gardening, working on cars, playing with dogs, etc. (Duke observed a whole engine rebuild this summer) . It's been a great life... UNTIL -

Duke has discovered chasing the chickens of the neighbor down the road. I cannot keep him home now, unless he is in the dog run (concrete edges to prevent digging out) or I am actively paying attention to him. I used to wake up for work, let the dogs out, use the ladies' room and then they would be sitting at the back door waiting for breakfast - except now, not for Duke. On several occations recently, he has escaped or been in the process of escaping when I've exited the ladies' room to bring breakfast. We've put a chain with a padlock on the gate so he can't open it, we have regular "perimeter walks" to fill holes near the fence (we don't care about the craters INSIDE - if it were just digging, well heck, we have acres to dig on), and now he's climbing the fence. And of course, he heads straight for our chicken neighbors at a full gallop. I am afraid he is going to get shot (I cannot blame the chicken owners if they do). Animal Control picked him up this week for escaping and going chicken chasing.

I am at a loss what to do. I don't want to keep him penned when the others have free range, but that is what I've been doing. Unless someone is actively playing with him, he has to be either in the house with us (which is not bad - he is a sweetheart dog - but he needs outside time, too) or in the pen. Do you have any suggestions? My other two dogs have stayed home even when Duke opened the gate (before we had it chained), but I am worried he will teach the others to go exploring and to discover chickens. I can understand that he can hear them all day long - even when I can't hear them, I will see his head suddenly lift and he will point towards them with this alert, I'm on the hunt, look (probably like how I look at chocolate). He probably can smell them, too - they are only a few houses down the road from us.

Duke is my Baby and there's got to be something to keep him home. He's a rescue dog, and I don't want to go back on my promise that he had a permanent home now (he had had a whole bunch of homes in the first year of his life) and wasn't a "disposable" dog any more. He's even featured on the weim page - portrait taken in the garden, of course - http://www.norcalweimrescue.org/Success_Stories.html

Anyway, sorry to be so longwinded. The last 30 days or so have been just aweful for both human and canines. And even worse for the chickens, too, I'm sure. As, you can probably tell, I am quite distressed. Suddenly WE are the "Bad Neighbors"! Any help is greatly appreciated!

Karla & Duke