Guscro -- Please take the time to read wildeflower's post above.
As painful as it is to lose birds and animals to predators, poison is not the answer. My grandfather had forty or so Black Star hens a few winters ago, and a coyote jumped the fence and killed every last one of them. He was mad as all get out--and I don't blame him for it. However, he used legal methods to trap and dispatch the predators that killed his birds. Not only does putting out poison often carry some serious legal ramifications, but it will put a lot of other animals at risk, too, including neighborhood dogs and federally protected raptors.
As poultry owners, we have an obligation to protect our flocks. We have a right to be upset, but we also have a right to take the proper precautionary methods. Free-range birds are always in danger, whether the danger is a coyote, neighbor dog, or hawk. If you're not able to watch your birds while they're out in the yard and don't keep them in a run or penned up, there will be fatalities--if not now as there have been, then later when you least expect it. The same truth applies to dogs and cats. This is not always ideal or appealing, but it's often what must be done to see some improvement.
If the foxes in your area show little fear of people, look into the regulations of animal damage control trapping to try and trap the foxes, or look into and hire a nuisance animal removal service to do it for you. If you choose not to do any trapping, don't allow them their presence to intimidate you or allow them to be within your sight wherever you are at a given time on your property. Make lots of noise, make them uncomfortable, and don't give them any reason to tolerate the sight of you. (If you become an intimidating presence or sight before traps are laid, the fox may be inclined to shy from the traps, but it depends on the circumstances.)
Best of luck.
