I have kept laying hens for several years and had the same problem.I put an apron made from 1 inch steel wire 18 inches wide around the bottom of my pen and used gutter spikes to fasten it down,next I bought the strongest electric fence charger I could find,I ran three strands of hotwire around the bottom of the pen about 9 inches apart,up the posts and 0ne strand around the top,several times during the first week I could hear a scream,bellow,roar, during the night coming from my chicken lot,I would smile and go back to sleep,I realize people have the same right as I to have pets but sadly some of them take no responsibility as pet owners to control their pets.The dogs are just doing what comes natural and we have to take what steps necessary to protect our flock,what ever it may be,Your wife did right in shooting the dogs,Its not an easy thing to do,She is a strong woman and one to be proud of